This was the first edition of the postseason where home-field advantage in the World Series was awarded to the league who won the MLB All-Star Game, a rule which lasted until 2016.
The postseason began on September 30, 2003, and ended on October 25, 2003, with the Marlins defeating the Yankees in six games in the 2003 World Series.
The Red Sox rallied from a two games to none series deficit to defeat the Athletics and advance to the ALCS for the first time since 1999.
The Athletics prevailed in a twelve-inning duel in Game 1, thanks to Ramón Hernández scoring Eric Chavez from a two-out bases-loaded bunt single off Derek Lowe.
Game 2 was the Athletics' tenth consecutive playoff win over the Red Sox in the wake of ALCS sweeps in 1988 and 1990, breaking the record for consecutive playoff wins against one team set by the New York Yankees against the Chicago Cubs with World Series sweeps in 1932 and 1938.
When the series shifted to Boston, the Red Sox avoided elimination thanks to a walk-off two-run home run from Trot Nixon in the bottom of the eleventh inning.
In Game 5, the Red Sox rallied late again with a four-run sixth inning to take the lead for good and advance to the ALCS.
Alex S. Gonzalez and Aramis Ramirez helped the Cubs jump out to a big lead early, which they did not relinquish as they won 5–1 to advance to the NLCS.
Game 2 was an offensive shootout which saw six pitching changes for each team, and the Marlins would prevail 9–5 to even the series headed to Miami.
In Boston for Game 3, the series was marred by a bench-clearing brawl, where Manny Ramírez took exception to a high pitch by Roger Clemens and charged the mound.
In Game 7, the Red Sox held a 5–2 lead going into the bottom of the eighth inning, however Boston manager Grady Little made a surprising move and decided not to pull starting pitcher Pedro Martinez.
The game lasted another two innings until the Yankees prevailed in the bottom of the eleventh thanks to a walk-off solo home run by Aaron Boone.
On the eighth pitch of his at bat, Luis Castillo hit a high foul ball toward the left field wall.
Cubs left fielder Moisés Alou (a former Marlin) headed toward the stands to catch the ball for the potential second out.
Miguel Cabrera then hit a ground ball toward Cubs shortstop Alex Gonzalez that could have ended the inning on a double play.
Gonzalez, who led all NL shortstops in fielding percentage, closed his glove too early and the ball landed in the dirt, allowing Cabrera to reach safely, loading the bases.
Prior was taken out of the game and replaced by Kyle Farnsworth, who intentionally walked Mike Lowell to load the bases.
Jeff Conine then hit a sacrifice fly to right field for the second out of the inning, allowing Cabrera to score from third and the other runners to each advance one base.
Farnsworth was taken out of the game and replaced by Mike Remlinger, who gave up a single to Pierre to score Mordecai from second base.
They would eventually redeem themselves in the 2016 NLCS, where the Cubs defeated the Los Angeles Dodgers in six games en route to a World Series title.
The Marlins became the first visiting team to win the World Series at Yankee Stadium since the Los Angeles Dodgers in 1981.