Five crucial MLB September series that could decide the 2026 playoff races

The 2026 MLB regular season is winding down with just three weeks remaining. We’ve got a pretty good idea for how most of the playoff picture is going to look once October hits, but there are some close races that you need to be paying attention to down the stretch. 

With SeatGeek serving as the Official Ticket Marketplace of MLB, we’ve been keeping a close eye on not just every playoff race, but every key series this season. With time winding down, these five matchups over the final three weeks of the regular season are worth keeping a close eye on and heading to the ballpark to watch. 

Most important MLB series to watch over the final three weeks of the 2026 season

From division races to Wild Card battles that could come down to the final weekend, these five series have the most potential to reshape the playoff picture before October.

Toronto Blue Jays vs. Baltimore Orioles: Sept. 11-13 (in Toronto), Sept. 21-23 (in Baltimore)

These AL East rivals are among the top contenders for the third and final AL Wild Card spot with the season winding down. The first of these two series is in Toronto, while Baltimore hosts the later one. 

The Blue Jays are 72-73 and are currently the first team out of the AL Wild Card picture as they trail the Guardians by a single game. The Orioles are 70-75 and have started to fade a bit of late as they have now dropped six of their last games, and they’re three games back of Cleveland. Baltimore is still in it, though, but the team must get hot soon, and getting six cracks at the Jays certainly will help. 

The Orioles have outscored the Blue Jays 42-33 this season in seven meetings, but Toronto owns a 4-3 series edge. These teams split a four-game set at the end of May before the Jays took two of three early in June, which is the last time they squared off. 

Chicago White Sox at Cleveland Guardians: Sept. 14-16

This is the series that could decide the AL Central. After a 10-1 shellacking of the Twins on Sunday and a Guardians loss on Monday, the White Sox hold a three-game lead over Cleveland. 

The Guardians just took three of four from Detroit over the weekend, including two walkoff wins, before falling to the O’s on Monday. They’re now 73-72 and hold the third and final AL Wild Card spot. Chicago, now 75-68, dropped two of three to Houston in its first series of September before rebounding with a series win over Minnesota. 

The Guardians will play host to this important three-game series next week. The run differential between these teams when they’ve met this year is nearly even (42 for the Sox, 41 for the Guards), but Chicago has had the upper hand, taking six of 10 matchups. The White Sox took both series in Chicago but these teams split a four-game set in Cleveland back in July. They met last month, with the White Sox winning the final two games after the Guardians took the opener. 

The Sox have been the biggest and best surprise in baseball this season, and this series is a chance for them to really cement themselves heading into the postseason. 

Toronto Blue Jays at Texas Rangers: Sept. 18-20

If any team is going to usurp the Guardians for the third and final Wild Card spot in the American League, there’s a good chance it’s either Toronto or Texas.

The Blue Jays have been one of the hottest teams in baseball of late, winning seven of their last 10, though they’ve dropped two in a row. They trail the Guardians by one game. The Rangers are right behind them at 71-73 and are 1.5 games back of Cleveland. Texas is also just two games back of Houston in the AL West, but those two don’t face each other again this regular season. 

The Rangers should feel good heading into this matchup for two reasons. First, Texas is at home, where it’s 39-32 on the year as of Sunday, Sept. 6. And second, the Rangers got a rare four-game sweep over the Blue Jays in Toronto at the end of June. 

This is a series that will have massive implications in the American League, both for the Wild Card race but also in the AL West depending how things start to unfold for both Texas and Houston over these final few weeks. 

Tampa Bay Rays at New York Yankees: Sept. 22-24 (doubleheader on Sept. 22)

The Rays have held control of the AL East for essentially the entire year, and at 85-58, they have a four-game lead over the Yankees (81-62). New York will get four cracks at Tampa Bay at home in each teams’ second-to-last series of 2026, which includes a doubleheader on Saturday, Sept. 22.

Both teams have been pretty rock steady this season, including in the second half. The Yankees are 27-20 since the All-Star Break while the Rays are 29-20 in the second half. Both teams have won six of their last 10 heading into this week of games, and the Yankees will get Aaron Judge back on Tuesday in his first game since May 31. 

The Rays have had the upper hand in this matchup this season, taking six of nine from their AL East rivals. They split a four-game set in Tampa Bay in early July, which was the last time these teams squared off, and they also swept New York at home in April. They split a brief two-game series in New York with the third game getting postponed, hence the need for a Saturday doubleheader. Depending how these teams do between now and then, this could be a matchup that helps determine both the winner of the AL East but also the No. 1 seed and homefield advantage in the American League playoff bracket. 

Arizona Diamondbacks at San Diego Padres: Sept. 25-27

We’ll end this with far and away the most intriguing final series of the year. These NL West rivals are neck and neck for the third and final NL Wild Card spot, and after Sunday, Arizona, 77-68, owns a slim half-game lead over the 76-68 Padres. Based on where these teams are in the standings and how most of the rest of the NL Wild Card contenders have fallen off – Miami and St. Louis are next up at four games back of Arizona – there’s a good chance this series decides the final playoff spot in the National League. 

San Diego got a big series win this weekend by taking two of three from the Yankees, and that came after losing three series in a row and seven of its previous nine games. Arizona won its series against Houston over the weekend after splitting a four-game series with the Giants and losing a series to Philadelphia. Both teams won series openers on Monday, with Arizona beating Kansas City and San Diego taking down Washington. 

Tiebreakers are always something to watch for in sports, but they’re usually less common in baseball given how many games are played. That could really come into play here, though, as these teams are currently locked up at 5-5 in the season series. So if, for example, the Padres enter this series one game back of the Diamondbacks and take two of three, they would end the year with the same record, but San Diego would have a 7-6 head-to-head edge and would get into the playoffs. Yeah, this race should be tight, and this series in particular may be really, really important.