With a 4-0 win over the Tampa Bay Rays, Houston clinched the AL West crown for the fifth time in six seasons.
The team entered Monday with a magic number of just one game to clinch the division.
The Astros could have clinched before their game was decided with the Rays due to Seattle starting its matchup against the Los Angeles Angels earlier in the day.
The Mariners defeated the Angels to delay the clinch just for a couple of hours.
Seattle was the Astros' closest rival record-wise, though, it looked more and more unlikely that the Mariners would not make up their 15-games deficit with three weeks of the season left.
The Astros also look poised to clinch the best record in the AL and homefield throughout their side of the postseason bracket.
After Monday's game, Houston's magic number to clinch the AL's top seed is at seven. The team is eight games up on the New York Yankees, who are having trouble closing out the AL East down the stretch.
If the season ended Monday, Houston would get a top-seed bye through the expanded wild-card round, which is a new MLB playoff concept that extends the number of teams entering the postseason from 10 to 12, with six teams in each league.
The Astros would face the winner of the No. 5 vs. No. 4 seed matchup, which is currently positioned as Tampa Bay vs. Toronto, in the AL Division Series.
Houston's regular season ends Wednesday, Oct. 5.
Meanwhile, you can get into gear for the playoffs with some AL West division championship swag.
The Astros said their Union Station Team Store is open for 24 hours.
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