The 2021 Seattle Mariners season was the 45th season in franchise history. The Mariners played their 22nd full season (23rd overall) at T-Mobile Park, their home ballpark in Seattle, Washington. The M's entered this season with the longest active playoff drought in the four major North American professional sports leagues, attempting to make their first postseason in twenty years. Seattle is the only current Major League Baseball (MLB) franchise without a World Series appearance. Despite posting a 90–72 record, their best since the 2003 season, the Mariners finished in second place in the American League West and were eliminated from postseason contention for the 20th consecutive season after the Boston Red Sox and New York Yankees clinched the Wild Card spots on the final day of the regular season. This season was the second time during their drought that the Mariners won two more regular season games than the World Series champions.
Regular season In the Mariners' 1–0 loss to the Los Angeles Dodgers on April 20, the two teams combined for three hits, tying the record for the fewest in an interleague game set by the Boston Red Sox and Montreal Expos in . As that game featured a home run, a double, and a single, and the Mariners/Dodgers games featured just a double and two singles, it broke the record for fewest total bases in a regular-season interleague game.
Pitcher Yusei Kikuchi was the team's lone MLB All-Star Game selection.
On September 1, general manager Jerry Dipoto was promoted to president of baseball operations.
Standings
American League West
American League playoff standings
Record against opponents
Game log
|- style="background:#bfb;" | 1 || April 1 || Giants || 8–7 || Misiewicz (1–0) || Álvarez (0–1) || — || 8,174 || 1–0 || W1 |- style="background:#fbb;" | 2 || April 2 || Giants || 3–6 || Peralta (1–0) || Steckenrider (0–1) || McGee (1) || 8,392 || 1–1 || L1 |- style="background:#bfb;" | 3 || April 3 || Giants || 4–0 || Flexen (1–0) || Webb (0–1) || Montero (1) || 8,651 || 2–1 || W1 |- style="background:#fbb;" | 4 || April 5 || White Sox || 0–6 || Rodón (1–0) || Sheffield (0–1) || — || 6,436 || 2–2 || L1 |- style="background:#fbb;" | 5 || April 6 || White Sox || 4–10 || Giolito (1–0) || Margevicius (0–1) || — || 7,980 || 2–3 || L2 |- style="background:#bfb;" | 6 || April 7 || White Sox || 8–4 || Vest (1–0) || Foster (0–1) || — || 7,429 || 3–3 || W1 |- style="background:#fbb;" | 7 || April 8 || @ Twins || 2–10 || Berríos (2–0) || Gonzales (0–1) || — || 9,675 || 3–4 || L2 |- style="background:#bfb;" | 8 || April 10 || @ Twins || 4–3 || Graveman (1–0) || Rogers (0–1) || Middleton (1) || 9,817 || 4–4 || W1 |- style="background:#bfb;" | 9 || April 11 || @ Twins || 8–6 || Steckenrider (1–1) || Colomé (0–1) || Montero (2) || 9,792 || 5–4 || W2 |- style="background:#bbb;" | – || April 12 || @ Orioles || colspan=7| Postponed (Rain, makeup: April 13) |- style="background:#bfb;" | 10 || April 13 || @ Orioles || 4–3 || Montero (1–0) || Scott (0–1) || Graveman (1) || N/A || 6–4 || W3 |- style="background:#fbb;" | 11 || April 13 || @ Orioles || 6–7 || Valdez (2–0) || Sadler (0–1) || — || 4,147 || 6–5 || L1 |- style="background:#bbb;" | – || April 14 || @ Orioles || colspan=7| Postponed (Rain, makeup: April 15) |- style="background:#bfb;" | 12 || April 15 || @ Orioles || 4–2 || Gonzales (1–1) || Scott (0–2) || Graveman (2) || N/A || 7–5 || W1 |- style="background:#bfb;" | 13 || April 15 || @ Orioles || 2–1 || Dunn (1–0) || Zimmermann (1–1) || Middleton (2) || 5,060 || 8–5 || W2 |- style="background:#bfb;" | 14 || April 16 || Astros || 6–5 || Misiewicz (2–0) || Stanek (0–1) || — || 8,967 || 9–5 || W3 |- style="background:#fbb;" | 15 || April 17 || Astros || 0–1 || Greinke (2–1) || Flexen (1–1) || Pressly (1) || 8,960 || 9–6 || L1 |- style="background:#bfb;" | 16 || April 18 || Astros || 7–2 || Newsome (1–0) || Odorizzi (0–2) || — || 8,959 || 10–6 || W1 |- style="background:#bfb;" | 17 || April 19 || Dodgers || 4–3 || Sheffield (1–1) || May (1–1) || Montero (3) || 8,999 || 11–6 || W2 |- style="background:#fbb;" | 18 || April 20 || Dodgers || 0–1 || Urías (3–0) || Gonzales (1–2) || Jansen (4) || 8,998 || 11–7 || L1 |- style="background:#bfb;" | 19 || April 22 || @ Red Sox || 7–3 || Montero (2–0) || Hernández (0–1) || — || 4,617 || 12–7 || W1 |- style="background:#fbb;" | 20 || April 23 || @ Red Sox || 5–6 || Sawamura (1–0) || Kikuchi (0–1) || — || 4,646 || 12–8 || L1 |- style="background:#bfb;" | 21 || April 24 || @ Red Sox || 8–2 || Flexen (2–1) || Eovaldi (3–2) || — || 4,621 || 13–8 || W1 |- style="background:#fbb;" | 22 || April 25 || @ Red Sox || 3–5 || Rodríguez (4–0) || Margevicius (0–2) || Barnes (4) || 4,510 || 13–9 || L1 |- style="background:#fbb;" | 23 || April 26 || @ Astros || 2–5 || Urquidy (1–2) || Sheffield (1–2) || Pressly (2) || 11,862 || 13–10 || L2 |- style="background:#fbb;" | 24 || April 27 || @ Astros || 0–2 || Javier (3–0) || Gonzales (1–3) || Pressly (3) || 14,413 || 13–11 || L3 |- style="background:#fbb;" | 25 || April 28 || @ Astros || 5–7 || Smith (1–1) || Montero (2–1) || Stanek (1) || 12,707 || 13–12 || L4 |- style="background:#bfb;" | 26 || April 29 || @ Astros || 1–0 || Kikuchi (1–1) || García (0–3) || Graveman (3) || 14,149 || 14–12 || W1 |- style="background:#bfb;" | 27 || April 30 || Angels || 7–4 || Steckenrider (2–1) || Heaney (1–2) || — || 8,632 || 15–12 || W2
|- style="background:#fbb;" | 28 || May 1 || Angels || 5–10 || Canning (2–2) || Newsome (1–1) || — || 8,993 || 15–13 || L1 |- style="background:#bfb;" | 29 || May 2 || Angels || 2–0 || Sheffield (2–2) || Bundy (0–3) || Montero (4) || 9,000 || 16–13 || W1 |- style="background:#fbb;" | 30 || May 3 || Orioles || 3–5 || Sulser (1–0) || Misiewicz (2–1) || Valdez (7) || 5,776 || 16–14 || L1 |- style="background:#bfb;" | 31 || May 4 || Orioles || 5–2 || Montero (3–1) || Lakins (1–3) || — || 6,504 || 17–14 || W1 |- style="background:#fbb;" | 32 || May 5 || Orioles || 0–6 || Means (4–0) || Kikuchi (1–2) || — || 6,742 || 17–15 || L1 |- style="background:#bfb;" | 33 || May 7 || @ Rangers || 5–4 || Flexen (3–1) || Sborz (3–2) || Graveman (4) || 26,047 || 18–15 || W1 |- style="background:#fbb;" | 34 || May 8 || @ Rangers || 8–9 || King (4–1) || Misiewicz (2–2) || Kennedy (10) || 26,616 || 18–16 || L1 |- style="background:#fbb;" | 35 || May 9 || @ Rangers || 2–10 || Dunning (2–2) || Sheffield (2–3) || — || 30,632 || 18–17 || L2 |- style="background:#fbb;" | 36 || May 11 || @ Dodgers || 4–6 || Cleavinger (1–3) || Montero (3–2) || Jansen (6) || 15,570 || 18–18 || L3 |- style="background:#fbb;" | 37 || May 12 || @ Dodgers || 1–7 || Urías (5–1) || Dunn (1–1) || — || 15,586 || 18–19 || L4 |- style="background:#fbb;" | 38 || May 13 || Indians || 2–4 || Plesac (3–3) || Gilbert (0–1) || Shaw (1) || 9,880 || 18–20 || L5 |- style="background:#bfb;" | 39 || May 14 || Indians || 7–3 || Flexen (4–1) || Civale (5–1) || Montero (5) || 10,014 || 19–20 || W1 |- style="background:#bfb;" | 40 || May 15 || Indians || 7–3 || Sheffield (3–3) || McKenzie (1–2) || — || 10,311 || 20–20 || W2 |- style="background:#bfb;" | 41 || May 16 || Indians || 3–2 || Sewald (1–0) || Bieber (4–3) || Graveman (5) || 10,287 || 21–20 || W3 |- style="background:#fbb;" | 42 || May 17 || Tigers || 1–4 || Mize (3–3) || Kikuchi (1–3) || Fulmer (3) || 7,201 || 21–21 || L1 |- style="background:#fbb;" | 43 || May 18 || Tigers || 0–5 || Turnbull (3–2) || Dunn (1–2) || — || 6,883 || 21–22 || L2 |- style="background:#fbb;" | 44 || May 19 || Tigers || 2–6 || Skubal (1–6) || Gilbert (0–2) || — || 8.462 || 21–23 || L3 |- style="background:#fbb;" | 45 || May 21 || @ Padres || 1–16 || Paddack (2–3) || Flexen (4–2) || — || 15,250 || 21–24 || L4 |- style="background:#fbb;" | 46 || May 22 || @ Padres || 4–6 || Stammen (3–1) || Sheffield (3–4) || Melancon (16) || 15,250 || 21–25 || L5 |- style="background:#fbb;" | 47 || May 23 || @ Padres || 2–9 || Darvish (5–1) || Misiewicz (2–3) || — || 15,250 || 21–26 || L6 |- style="background:#bfb;" | 48 || May 24 || @ Athletics || 4–2 || Kikuchi (2–3) || Montas (5–4) || Middleton (3) || 3,019 || 22–26 || W1 |- style="background:#bfb;" | 49 || May 25 || @ Athletics || 4–3 || Sewald (2–0) || Irvin (3–6) || Montero (6) || 2,865 || 23–26 || W2 |- style="background:#fbb;" | 50 || May 26 || @ Athletics || 3–6 || Kaprielian (2–0) || Dugger (0–1) || Diekman (6) || 3,571 || 23–27 || L1 |- style="background:#bfb;" | 51 || May 27 || Rangers || 5–0 || Flexen (5–2) || Allard (1–1) || — || 9,008 || 24–27 || W1 |- style="background:#bfb;" | 52 || May 28 || Rangers || 3–2 || Sheffield (4–4) || Lyles (2–4) || Swanson (1) || 10,605 || 25–27 || W2 |- style="background:#bfb;" | 53 || May 29 || Rangers || 3–2 || Zamora (1–0) || Foltynewicz (1–5) || Montero (7) || 11,071 || 26–27 || W3 |- style="background:#bfb;" | 54 || May 30 || Rangers || 4–2 || Kikuchi (3–3) || Yang (0–3) || Middleton (4) || 11,198 || 27–27 || W4 |- style="background:#bfb;" | 55 || May 31 || Athletics || 6–5 || Zamora (2–0) || Trivino (2–2) || — || 11,112 || 28–27 || W5
|- style="background:#fbb;" | 56 || June 1 || Athletics || 6–12 || Luzardo (2–3) || Sewald (2–1) || — || 9,160 || 28–28 || L1 |- style="background:#fbb;" | 57 || June 2 || Athletics || 0–6 || Manaea (4–2) || Flexen (5–3) || — || 9,588 || 28–29 || L2 |- style="background:#bfb;" | 58 || June 3 || @ Angels || 6–2 || Sheffield (5–4) || Canning (4–4) || — || 9,714 || 29–29 || W1 |- style="background:#fbb;" | 59 || June 4 || @ Angels || 2–3 || Ohtani (2–1) || Santiago (0–1) || Iglesias (10) || 15,141 || 29–30 || L1 |- style="background:#fbb;" | 60 || June 5 || @ Angels || 5–12 || Cobb (4–2) || Steckenrider (2–2) || — || 15,071 || 29–31 || L2 |- style="background:#bfb;" | 61 || June 6 || @ Angels || 9–5 || Gilbert (1–2) || Sandoval (0–2) || — || 12,833 || 30–31 || W1 |- style="background:#fbb;" | 62 || June 8 || @ Tigers || 3–5 || Boyd (3–6) || Gonzales (1–4) || Cisnero (2) || 9,081 || 30–32 || L1 |- style="background:#bfb;" | 63 || June 9 || @ Tigers || 9–6 || Chargois (1–0) || Norris (0–2) || — || 9,162 || 31–32 || W1 |- style="background:#fbb;" | 64 || June 10 || @ Tigers || 3–8 || Jiménez (1–0) || Sheffield (5–5) || — || 9,290 || 31–33 || L1 |- style="background:#fbb;" | 65 || June 11 || @ Indians || 0–7 || Civale (9–2) || Dunn (1–3) || — || 22,970 || 31–34 || L2 |- style="background:#fbb;" | 66 || June 12 || @ Indians || 4–5 || Karinchak (3–2) || Sewald (2–2) || — || 20,116 || 31–35 || L3 |- style="background:#bfb;" | 67 || June 13 || @ Indians || 6–2 || Gilbert (2–2) || Bieber (7–4) || — || 17,371 || 32–35 || W1 |- style="background:#bfb;" | 68 || June 14 || Twins || 4–3 || Sewald (3–2) || Robles (2–3) || Steckenrider (1) || 9,185 || 33–35 || W2 |- style="background:#bfb;" | 69 || June 15 || Twins || 10–0 || Flexen (6–3) || Happ (3–3) || — || 7,669 || 34–35 || W3 |- style="background:#fbb;" | 70 || June 16 || Twins || 2–7 || Thielbar (1–0) || Sheffield (5–6) || — || 8,098 || 34–36 || L1 |- style="background:#bfb;" | 71 || June 17 || Rays || 6–5 || Santiago (1–1) || Fairbanks (1–2) || — || 9,092 || 35–36 || W1 |- style="background:#bfb;" | 72 || June 18 || Rays || 5–1 || Kikuchi (4–3) || Wacha (1–2) || — || 12,654 || 36–36 || W2 |- style="background:#bfb;" | 73 || June 19 || Rays || 6–5 || Montero (4–2) || Feyereisen (3–3) || — || 14,772 || 37–36 || W3 |- style="background:#bfb;" | 74 || June 20 || Rays || 6–2 || Montero (5–2) || Castillo (2–4) || — || 18,172 || 38–36 || W4 |- style="background:#bfb;" | 75 || June 22 || Rockies || 2–1 || Sewald (4–2) || Kinley (1–2) || Graveman (6) || 12,879 || 39–36 || W5 |- style="background:#fbb;" | 76 || June 23 || Rockies || 2–5 || Márquez (6–6) || Sheffield (5–7) || Bard (10) || 11,141 || 39–37 || L1 |- style="background:#bfb;" | 77 || June 25 || @ White Sox || 9–3 || Kikuchi (5–3) || Rodón (6–3) || — || 32,189 || 40–37 || W1 |- style="background:#bbb;" | — || June 26 || @ White Sox || colspan=7| Suspended (Rain, continuation: June 27)