Seattle Mariners vs Houston Astros Prediction, Odds and Picks for Today, 09/21/25

Logan Gilbert is set to start Sunday’s matchup against the Houston Astros, and the Seattle Mariners’ right-hander is a large part why I think the Mariners are set up for success in this spot. Seattle has won the first 2 games of this crucial series with their divisional rivals, taking a 2-game lead on the division after the teams entered this series tied. I expect Seattle to finish off the road sweep in this game as they hold the lineup in better form, and the starter with a more proven track record. Gilbert is in good form with just 8 combined earned runs allowed across his last 5 starts. His 3.53 ERA in 120 innings is not indicative of how lethal he is on the mound, and I expect to see the best of Gilbert down the final stretch.

Jason Alexander served as a swingman for the Brewers in 2022 with 71.2 innings for them that season. He didn’t pitch again in the majors until this season, beginning the season with the Athletics. Houston picked him up and he has been an awesome piece of their rotation with a 2.76 ERA across 65.1 innings for the club. While his story is awesome and the unexpected production has been welcomed by the club, I am not a fan of his matchup in this spot and lean towards a win for the Mariners.

Seattle Mariners vs Houston Astros prediction: Mariners ML (-135) available at time of publishing. Playable to -14o odds.