Because inclusion in the Major League Baseball postseason is based upon the teams' regular-season records, procedures exist to break ties between teams.
Main article: One-game playoff
One-game tiebreakers are played between teams tied for a division championship or a league's second wild-card berth. These games are to be played the day after the season is scheduled to end. Home-field advantage is determined using the rules listed below ("Breaking Ties Without Playoff Games").
From the implementation of the wild-card in 1994 to the end of the 2011 season, a different rule was in place. Two teams tied for a division did not play a tiebreaker if their records were better than all non-division winners in their league. Instead, said tie was broken using the rules listed below ("Breaking Ties Without Playoff Games"). This scenario happened in the 2001 Major League Baseball season when the Houston Astros and St. Louis Cardinals tied for first place in the National League Central. The Astros were awarded the division title by virtue of a better head-to-head record against the Cardinals, while St. Louis received the wildcard berth.
With, however, the adoption of a second wild-card berth and a Wild Card Game beginning in the 2012 season, the non-division winner with the best record in the league faces possible elimination on the first day of the postseason. As a result, the tie-breaking rules were changed so that two teams tied for a division championship must play a tiebreaking game even if both teams have already qualified for the postseason. The team losing the tie-breaking game will now qualify for a wild-card berth only if its regular-season record is among the league's two best records for non-division-winners. If that team is tied for the second wild-card spot, a second tie-breaking game would then be played.
If, on the other hand, two teams are tied for the first wild-card spot, no tie-breaking game is played. Rather, the two teams simply play against each other in the Wild Card game, with home-field advantage awarded using tie-breaking rules described in the next section.
*all current references in mlb.com website indicate that this rule applies even for teams that are not in the same division.
If two champions from separate divisions have the same record, the tiebreaking procedure listed above is used to determine postseason seeding. No additional games are played.
Tied teams are designated as A, B, C, and D. Choice for one of these designations is first given to the team winning the tie-breakers (listed below). While A is usually the "best" designation, there are some scenarios where C has a different path to the postseason. If a division title is up for grabs, then those divisional teams will select from the first designations (A, B,...).
On Day 1, A will host B and C will host D (if there is no fourth team, C will be considered to have won this game). Games on Day 2 may occur as follows:
The order in which teams pick their designations (A, B, C, D) will be determined by the following 5-step tie-breaking system. If there is a tie for both wild card and division title spots, then the first designations will match teams competing for their division title.
If at any given step some, but not all, teams remain tied, then those teams that are still tied revert to Step 1.