The celebration -- or perhaps the relief -- will have to wait for the Astros.

Josh Reddick's two-run single spoiled the Mariners' shutout bid in the ninth inning for the second time in three games, but the tying and go-ahead runs were stranded on base as Seattle held on for a 3-2 win Wednesday night at T-Mobile Park that kept Houston's magic number to clinch a playoff berth at two.

• Box score

The Astros (28-28) will now have to wait until Friday to clinch a playoff spot, at the earliest. Their magic number is two over the Angels, who are off Thursday. So even if the Astros beat the Rangers on Thursday in Arlington, Houston's magic number will be reduced to one.

"It is what it is," Astros manager Dusty Baker said. "You can't reverse it and take it back. We just have to go back to the drawing board."

Houston starter Zack Greinke gave up three runs and eight hits in 4 2/3 innings in his shortest start since July 26 and continues to slide down the stretch, posting a 5.73 ERA in his last seven starts. The Astros, meanwhile, were befuddled by Mariners lefty Nick Margevicius, who held them scoreless for six innings, despite throwing his fastball, which averaged 88 mph, 71 percent of the time.

"We need to do a better job offensively; need to get better," Astros third baseman Alex Bregman said. "It's getting down to the end of the season, so we need to start swinging the bats a lot better."

The Astros have made it a habit recently for struggling starters to have their best games of the season against them, with Margevicius joining a list that includes Kyle Gibson and Jordan Lyles of the Rangers and Madison Bumgarner of the D-backs.

• Baker: Altuve will 'rise to the occasion'

"The young left-hander had us kind of eating out of his hand, because he was effectively wild," Baker said. "He would throw two or three balls and then throw some quality strikes. It was just a bad day at the ballpark. You hate to lose like that, especially when you had opportunities."

Stranding runners and the overall lack of offense has been a consistent theme for the Astros in the last month, which has seen them have to fight and claw for a playoff spot in a season when eight teams advance to the postseason in each league.

"In hitting, we talk about repeatability and being able to repeat your swing," Bregman said. "We need to repeat what we're doing at the plate when we're good. And we're not doing a good job of repeating consistently. For myself, mechanically, I've been bad. I'm working on it every single day and going to continue to do that. That's the only way for success to continually work."

Since starting 21-15, the Astros are 7-13 in their last 20 games. They're hitting .216 as a team in that stretch, including .191 with runners in scoring position, and averaging 3.4 runs per game. Houston was 1-for-9 with runners in scoring position Wednesday, including the bases loaded in the fifth.

"We're better than we're showing," Baker said. "I know [hitting coaches Alex] Cintron and [Troy] Snitker, they were pulling their hair out trying to figure out what's wrong and I'm trying to help. The guys are putting in the work and putting in the time. We hit a couple of balls hard for outs and then the strikeouts at the wrong time are killing us right now."