Since 2022, all ties in the standings -- for a division title or Wild Card spot, or to determine playoff seeding -- have been determined solely by a series of mathematical tiebreakers, rather than on the field. A full breakdown of the current methodology can be seen here, but to summarize, the top three elements are, in order: head-to-head record, intradivision record (i.e. within the same division) and then record against opponents in the same league but a different division.
This means that a team’s head-to-head record against its rivals is more important than ever, as it can very well determine who plays deep into October and who goes home after Game 162. Consider what happened in 2022, when the Braves and Mets finished with identical 101-61 records, but Atlanta won the NL East title by virtue of going 10-9 against New York, which then fell to San Diego in the best-of-three Wild Card Series.
Because of this, MLB.com was tracking the progress of various tiebreaker scenarios throughout the home stretch of the 2023 regular season.
In the end, there were no chaotic three-team (or even four-team) tie scenarios. However, tiebreakers did come into play in terms of finalizing the postseason field.
Most notably, the Astros and Rangers tied for the best record in the AL West, at 90-72, with Houston winning and Texas losing on Sunday. Because the Astros won nine of the teams' 13 matchups in 2023, they claimed the tiebreaker and thereby their sixth AL West crown since 2017.
That makes the Astros the No. 2 seed in the AL playoffs, giving them a bye into the Division Series. The Rangers, on the other hand, fell to the No. 5 seed, forcing them into being the road team in a best-of-three Wild Card Series against the 99-win Rays.
A tiebreaker was also a factor in NL playoff seeding. The D-backs lost on Sunday, finishing 84-78. The Marlins also lost, making them 84-77, with one fewer completed game. (Miami's game on Thursday against the Mets at Citi Field was suspended in the ninth inning.) While that game was due to be resumed on Monday, doing so would not affect seeding. That's because, with the Marlins going 4-2 against the D-backs this season, they would win a tiebreaker even if they lost the suspended game to finish with an identical 84-78 record.
Therefore, the Marlins are in line to be the No. 5 NL seed (playing at Philadelphia in the Wild Card Series), while the D-backs would be the No. 6 seed (playing at Milwaukee).