Major League Baseball expanded its playoff format to 10 teams Friday, adding a second wild-card in each league.
The decision establishes a new one-game, wild-card round in each league between the teams with the best records who are not division winners, meaning a third-place team could win the World Series.
This is the only change in baseball's playoff structure since the 1995 season, when wild-card teams were first added.
"This change increases the rewards of a division championship and allows two additional markets to experience playoff baseball each year," Commissioner Bud Selig said in a statement.
If these rules had been in place last season, the Atlanta Braves would have made the playoffs in the National League, and the Boston Red Sox would have qualified in the American League. Instead, each missed the postseason by a game, going down with historic September swoons.
"The players are eager to begin playing under this new format in 2012, and they look forward to moving to full realignment in 2013," said players' union executive director Michael Weiner.
As part of baseball's labor deal, the Houston Astros will switch to the American League in 2013, creating two 15-team leagues with three divisions each. Players wanted the change to give every division the same chance to make the playoffs.
Baseball's postseason was officially born in 1903, when the American League's Boston Americans beat the National League's Pittsburgh Pirates in the first World Series.
Until 1969, the match between the two league champs was the only postseason action. That year, each league split into two divisions and four teams made the playoffs. The current format — three division champs and a wild-card team in each league — was adopted in 1995.