The 2005 Houston Astros season was the 44th season for the Major League Baseball (MLB) franchise located in Houston, Texas, their 41st as the Astros, 44th in the National League (NL), 12th in the NL Central division, and sixth at Minute Maid Park. The Astros entered the season with a 92–70 record, having qualified for their first-ever Wild Card title, runners-up in the NL Central, and 13 games behind the division-champion and NL pennant-winning St. Louis Cardinals. However, the Astros' season halted after defeat in a classic, 7-game National League Championship Series (NLCS) to the Cardinals.

On April 5, Roy Oswalt made his third consecutive Opening Day start for the Astros, who hosted St. Louis, but were defeated, 7–3. In the amateur draft, the Astros' first round selections included left-handed pitcher Brian Bogusevic (24th overall) and outfielder Eli Iorg (38th). On June 25, the Astros retired the uniform number 24 worn by former outfielder Jimmy Wynn, the first player in club history to steal 40 bases (1965) and hit 30 home runs (1967) in one season. With expectations of a deeper postseason run in 2005, Houston initially underperformed, starting at 15–30.

Four Astros were selected to the MLB All-Star game, including pitchers Roger Clemens, Brad Lidge, and Oswalt, and third baseman Morgan Ensberg. It was the 11th career selection for Clemens, and first for each of Oswalt, Lidge, and Ensberg. On September 10, Craig Biggio became the 13th major leaguer to attain 600 doubles.

The Astros rebounded to win 74 of the final 117 games ( winning percentage) and posted an 89–73 overall record, runners-up in the NL Central for a fourth consecutive season and 11 games behind the repeat division-champion St. Louis Cardinals. In the Wild Card race, the Astros finished one game ahead of the Philadelphia Phillies to obtain both their second-consecutive NL Wild Card title and playoff berth. It was the Astros' sixth playoff appearance in a span of nine seasons. The ninth postseason appearance overall in franchise history, it was their second wild card qualification.

The Astros faced the Atlanta Braves for their fifth matchup in nine seasons in the National League Division Series (NLDS) format. Houston triumphed in a second consecutive NLDS, capped by the series-ending walk-off home run by Chris Burke in the 18th inning. A second consecutive rematch with St. Louis in the NLCS awaited Houston, this time yielding a 4-games-to-2 victory for their first-ever NL pennant and World Series appearance. Oswalt, who won both of his starts and allowed just 2 earned runs over 14 innings pitched (IP) for a 1.29 earned run average (ERA), was recognized as NLCS MVP. However, the Astros were swept by the Chicago White Sox, 4 games to 0, in the World Series.

Clemens won the regular season NL earned run average (1.87 ERA) title. Biggio was recognized with the Hutch Award, Ensberg with a Silver Slugger Award, and center fielder Willy Taveras as the Players Choice Award winner for NL Outstanding Rookie, The Sporting News NL Rookie of the Year, and to the Topps All-Rookie Team. Joining Wynn in receiving career accolades were Biggio and Jeff Bagwell as inductees into the Texas Sports Hall of Fame and recipients of Baseball Americas Lifetime Achievement Award, with executive Tal Smith also being conferred the latter honor.

The 2005 season was the Astros' final playoff appearance as a National League team, and for the next ten seasons, until 2015, after having transitioned to the American League.

Offseason Summary The Houston Astros concluded the 2004 epoch with a record, 13 games behind the NL Central division champion St. Louis Cardinals. In the NL Wild Card race, the Astros finished a game ahead of the San Francisco Giants to capture their first-ever Wild Card title. The Astros won the National League Division Series (NLDS), 3-games-to-2, over the Atlanta Braves. Hence, the Astros triumphed in a playoff series for the first time in franchise history, while also defeating Atlanta in a playoff series on their fourth attempt. The team set an all-time regular season home attendance record of 3,087,872, surpassing 3.056,139 in , the first time they had reached 3 million. Right-hander Roger Clemens became the second Astro to win the Cy Young Award, the seventh of his career, and Carlos Beltrán became the second Astro to join the 30–30 club, following Jeff Bagwell.

In February 2005, longtime Astros players Jeff Bagwell and Craig Biggio were jointly inducted into the Texas Sports Hall of Fame.

Outfielder Lance Berkman missed the start of the regular season recuperating from knee surgery.

Transactions January 7, 2005: Adam Riggs was signed as a free agent with the Houston Astros. January 7, 2005: Turk Wendell was signed as a free agent with the Houston Astros. January 23, 2005: John Franco signed as a free agent with the Houston Astros. February 11, 2005: Trenidad Hubbard was signed as a free agent with the Houston Astros.

Regular season Summary April

+ Opening Day starting lineup Player Position 28 Adam Everett Shortstop 7 Craig Biggio Second baseman 5 Jeff Bagwell First baseman 14 Morgan Ensberg Third baseman 30 Luke Scott Left fielder 16 Jason Lane Right fielder 11 Brad Ausmus Catcher 1 Willy Taveras Center fielder 44 Roy Oswalt Pitcher Venue: Minute Maid Park • St. Louis 7, Houston 3 Sources:

Houston's 44th season arose with Roy Oswalt on the mound, who bore uniform number 44. The Astros hosted the St. Louis Cardinals, also the last team they had faced in defeat in a classic, seven-game 2004 National League Championship Series (NLCS). St. Louis countered with Chris Carpenter. Oswalt was not sharp, as he yielded six runs over six innings, including serving home runs to Jim Edmonds and Reggie Sanders. Oswalt took the defeat in a 7–3 loss. Craig Biggio doubled among three hits and drove in each of Houston's tallies.

On April 16, center fielder Willy Taveras cranked his first major league home run, during the bottom of the seventh off right-hander Jorge Sosa of the Atlanta Braves. A solo shot at Minute Maid Park, it gave the Astros an insurance run to increase their lead to 5 to 3. Five-to-three stood as the final score. Taveras also drew a base on balls, pilfered a base, and scored twice. Brandon Backe earned the quality start and first victory of the season, tossing seven innings in which he scattered seven hits, one walk, and struck out eight. John Franco (2) and Russ Springer (2) each worked a scoreless inning to earn the hold, and Brad Lidge followed by converting his fourth save.

On April 23, the Astros lost a third consecutive 1–0 decision in extra innings started by Roger Clemens. Clemens had surrendered just one earned run through four starts for a 0.32 earned run average (ERA).

The Astros, hosting the Chicago Cubs on April 29, featured a matchup between Clemens and fellow 300-game winner, Greg Maddux. Clemens worked 7 innings with three runs allowed and four strikeouts, while Maddux surrendered two runs over six innings, striking out three. First baseman Jeff Bagwell, who was playing through injury, hit his final major league home run against Maddux on April 29, tying him for the most against any pitcher with seven. With the contest tied 2–2, Conroe native Jeromy Burnitz led off the seventh with a home run, allowing Maddux to get the win as the Cubs won, 3–2. The 306th win of Maddux' career, Clemens entered the game with 329. The Clemens–Maddux duel was the first time in the major leagues that two pitchers who had already attained 300 or more career wins faced each other since Don Sutton of the California Angels and Steve Carlton of the Minnesota Twins on August 4, 1987. It was the first such matchup in the National League (NL) since July 21, 1892, when Tim Keefe of the Philadelphia Phillies pitched against Jim "Pud" Galvin of the St. Louis Browns.

May

Mike Lamb swatted his first career grand slam on May 1, off Mark Prior of the Chicago Cubs, a go-ahead drive to give Houston the 5–3 edge. Later in the fifth, Adam Everett took Prior deep for three more tallies. Lamb picked up another RBI the next inning off Glendon Rusch, singling in Biggio. Oswalt (4–2) diffused 10 Cubs hits and three runs over five innings to pick up the victory. This was Lamb's second career five-RBI bout.

On May 5, Jeff Bagwell removed himself from the lineup. It was later announced that he would undergo capsular release surgery on his arthritic right shoulder with the goal of extending his career.

Filling in for Bagwell, on May 15, Morgan Ensberg launched a career day, blasting three home runs with 5 RBI to lead the way for the Astros, who routed the San Francisco Giants, 9–0. He became the eighth player in team history to crank three home runs in a game, and first since Richard Hidalgo on September 16, 2003. Ensberg also stroked his third career four-hit game, and both of the three home runs and five RBI established single-game career highs.

After another defeat as of May 24, the Astros occupied last place in the NL Central with a performance, 14 games behind the first-place Cardinals. This was Houston's seventh consecutive defeat for the team's longest losing streak of the season.

The Astros won over the Cubs on May 25 at Wrigley Field, led by seven solid innings from Brandon Backe (4–3), who defeated Greg Maddux (2–3). Turning in a quality start, Backe surrendered seven hits, one walk, and one run over seven frames, singled at the plate, and scored. Ensberg (9) took Maddux deep during the fifth inning, and Lance Berkman tallied two hits and an RBI. Backe and Willy Taveras each pilfered a base.

June On June 7, Chris Burke swatted his first Major League home run, during the seventh inning off Pedro Martinez of the New York Mets. Burke's home run ended Martinez' no-hit bid at innings. To this point, no Mets pitcher had ever tossed a no-hitter. Martinez (7–1) otherwise remained dominant, striking out 12 Astros in a two-hit complete game to outduel Roy Oswalt (6–7) and lead a 3–1 Mets' victory. Martinez' effort earned a game score of 90.

Retirement of Jim Wynn's uniform number 24

During a pre-game ceremony on June 25, the club officially retired uniform number 24,''' donned by former outfielder Jimmy Wynn. Dubbed "The Toy Cannon," the Wynn embodied the Colt.45s/Astros' original slugger, slamming 291 home runs during his 15-year career, including 223 with Houston—a franchise record that remained until Bagwell surpassed him in 1999. A native of the Cincinnati metropolitan area, Wynn signed out of high school with the Reds in 1962. Later that year, Houston selected him in the first-year player draft. Wynn began his major league career and spent 11 seasons with Houston from 1963 to 1973 prior to playing for Los Angeles, New York, Atlanta, and Milwaukee.

An excellent blend of power, speed, and patience, some of Wynn's distinctions included becoming the first Astros player to connect for three home runs in one game (June 15, 1967), the first to hit 30 home runs in a season (August 23, 1967), their first 40-stolen base bandit (43 in 1965), and, in 1969, a then-NL record tying 148 bases on balls fortified with an on-base streak of 52 games which tied for sixth in NL history. Following the 1973 campaign, Wynn departed Houston ranked among club leaders in hits (1,291), home runs and runs batted in (719 RBI).

Rest of June