"I felt like I made a lot of quality pitches that were somewhere near the zone, but unfortunately put too many men on base and got in some bad counts and made some mistakes and got behind," he said. "They, obviously, put them over the wall.
"Overall, I'm starting to feel better. I'm getting my [velocity] back and felt good up until that last pitch. I feel like I've still got a lot of stamina and I've got to go out there and do a better job. My job is to get 21 outs at least and I didn't do that tonight. There's definitely some things I can work on still."
Martin hit a solo homer to right field in the third, which was the only hit Fister allowed through three innings. Seager walloped a solo homer in the fourth to put the Mariners ahead, 2-1. Fister's allowed five home runs in 22 2/3 innings.
"I feel behind Seager and put him in a good hitter's count and tried challenging him with my best and I left it over the middle," he said. "He does what he does. I've known him for a long time, and that's what he does. He takes a good hack and puts a swing on the ball. The other one, I threw a changeup and it just kind of stayed still. Good velocity on it, but no depth to it. Unfortunately, he did what he did."
Fister pitched around leadoff walks in the first and second and escaped trouble when he walked a pair in the third. His one-out walk to Seth Smith in the fifth proved to be costly because it pushed Ketel Marte to second base, and Marte scored what turned out to be the winning run on a Robinson Cano single.
"Doug Fister kept us in the game for the most part," manager A.J. Hinch said.
Brian McTaggart has covered the Astros since 2004, and for MLB.com since 2009. Follow @brianmctaggart on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.