Early in 2003 , Clemens announced his retirement, effective at the end of that season. On June 13, 2003, pitching against the St. Louis Cardinals in Yankee Stadium , Clemens recorded his 300th career win and 4,000th career strikeout, the only player in history to record both milestones in the same game. [ citation needed ] The 300th win came on his fourth try; the Yankee bullpen had blown his chance of a win in his previous two attempts. He became the 21st pitcher ever to record 300 wins and the third ever to record 4,000 strikeouts, joining Nolan Ryan (5,714) and Steve Carlton (4,136). Randy Johnson (4,875) has since also joined the 4,000 strikeout club. His career record upon reaching the milestones was 300–155; his record at the end of the season was 310–160 with 4,099 strikeouts. Clemens finished the season with a 17–9 record and a ERA.
"... I became a great hitter because of my mental preparation. This is a thinking man's game. You can be the strongest dude alive and you're not going to be able to hit a sinker with 40,000 people screaming at you. That's what really makes me mad when I think about the way I will be remembered. They're only going to remember my power. They're not going to remember the hours and hours and hours of work in the film room. They're not going to remember the BP. They're not going to remember me for my intelligence. Despite all I've done in this game, I'm just the big DH from the Dominican. They turn you into a character, man.''
The Red Sox faced the St. Louis Cardinals in the 2004 World Series . The Cardinals had posted the best record in the major leagues that season, and had previously defeated the Red Sox in the 1946 and 1967 Series, with both series going seven games. The third time would be the charm, however, as the momentum and confidence Boston had built up in the ALCS would overwhelm St. Louis. The Red Sox began the Series with an 11–9 win, marked by Mark Bellhorn 's game-winning home run off Pesky's Pole . He later on said that he "just did what he needed to do." It was the highest scoring World Series opening game ever (breaking the previous record set in 1932 ). The Red Sox would go on to win Game 2 in Boston (thanks to another sensational performance by the bloody-socked Schilling). The Red Sox won both these games despite making 4 errors in each game. In Game 3, Pedro Martínez shut out the Cardinals for seven innings. The Cardinals only made one real threat — in the third inning when they put runners on second and third with no outs. However, the Cardinals' rally was killed by pitcher Jeff Suppan 's baserunning gaffe. With no outs, Suppan should have scored easily from third on a Larry Walker ground ball to second baseman Bellhorn, who was playing back, conceding the run. But as Bellhorn threw out Walker at first base, Suppan inexplicably froze after taking several steps toward home and was thrown out by Sox first baseman David Ortiz as he scrambled back to third. The double play was devastating for St. Louis. The Red Sox needed one more game to win their first championship since the 1918 World Series . In Game Four the Red Sox did not allow a run, and the game ended as Édgar Rentería (who would become the 2005 Red Sox starting SS) hit the ball back to Keith Foulke. (This was the second time that Rentería had ended a Series, as he had won it for the Marlins seven years prior in the 1997 World Series .) After Foulke lobbed the ball to Doug Mientkiewicz, the Sox had won their first World Championship in 86 years. The Sox held the Cardinals' offense (the best in the NL in 2004) to only three runs in the last three games, never trailing in the Series. Manny Ramírez was named World Series MVP. The Red Sox won Game Four of the series on October 27, eighteen years to the day from when they lost to the New York Mets in the 1986 World Series . In fact, it came 18 years to the day they lost their last World Series game, as they would sweep the 2004 series.