Astros vs. Mariners: What to know about crucial series with AL West lead, tiebreaker on the line

The Seattle Mariners and Houston Astros begin a pivotal three-game series Friday night that very well may determine who wins the American League West in 2025. The clubs will meet at Daikin Park, in Houston, knotted in more ways than one. Not only do they have identical 84-69 records, but they’ve also split their previous 10 head-to-head matchups. The winner of this series will be in first place and own the tiebreaker by Sunday night.

Series don’t get much bigger than this, and so CBS Sports is taking the opportunity to provide you with all you need to know heading into Friday’s opener. Let’s start with some vital information:

Now, onward to a few storylines of interest.

1. Tiebreaker at stake

As mentioned in the introduction, the Mariners and Astros have each won five of their 10 first head-to-head matchups this year. You don’t need a calculator or a spreadsheet to realize that, with three games left, one team is going to walk away with the season series. 

In turn, said team will gain an advantage: the tiebreaker. MLB did away with Game 163 scenarios when it expanded the playoffs. Ties are now determined, foremost, by head-to-head play. In effect, whichever team prevails this weekend — be it by a 2-1 series win or a sweep — will effectively add a game to their lead, since the other team will have to win the division outright or not at all.

2. Mariners enter hot

The Mariners will come into play having won 11 of their last 12 games, in the process eliminating what was a 3 ½-game Astros’ advantage in the West. That tear comes after the Mariners started September with an 0-4 stretch. Even at the time we here at CBS Sports noted they continued to have a real chance at overtaking the Astros thanks to a hidden advantage: their schedule.

Here’s some of what we wrote:

The kicker in all of this is that the Mariners still have a clear pathway to the division crown. They have one of the weakest remaining schedules in baseball, according to Tankathon’s math, with their opponents winning just 47.3% of their games. The Astros have closer to an average-strength schedule to play, with their own opponents winning exactly 50% of their games to date. 

Sure enough, since the publication of that paragraph the Mariners have won or swept a series against the Atlanta Braves, St. Louis Cardinals, Los Angeles Angels and Kansas City Royals — none of whom will be playing in October. The Astros meanwhile, have had to square off with the Toronto Blue Jays, Texas Rangers (twice), and a shared foe, in the Braves, and have a 7-4 record to show for their efforts.

3. Astros down several key players, but get Paredes back

No matter how the next 10 days play out, the story of the Astros’ season will remain focused on the absurd amount of injuries they’ve endured. According to Baseball Prospectus’ numbers, the Astros are one of just two teams to lose more than 2,000 player games to the IL this season — the other club being the Los Angeles Dodgers.

As of Friday, the Astros are down an entire starting rotation (including Luis Garcia, Ronel Blanco, and Hayden Wesneski), their closer (Josh Hader), and a starting position players (Brendan Rodgers). There’s also the matter of slugger Yordan Alvarez, who was forced to leave a game earlier this week after injuring his ankle while crossing the plate. (It should be noted that Alvarez isn’t on the IL, though his status remains in doubt.) The good injury news for Houston, though, is that All-Star infielder Isaac Paredes is set to return this weekend after missing the last two months with a hamstring strain.

That the Astros are even in this position — entering the final nine games of their schedule with a real chance at winning the division — is a testament to this club’s resilience and resourcefulness.