Seattle's playoff hopes took another hit, as Marisnick had a three-run homer for the second straight game and Alex Presley drove in two runs to lead the Astros to an 8-3 win over the Mariners on Sunday.
Marisnick was acquired in July in a trade that sent right-hander Jarred Cosart to the Marlins. He hit just .167 in 14 games this season for Miami, but is batting .276 with three homers and 19 RBIs in 45 games for the Astros.
"It's on-the-job training really for him learning up here at the big league level for the first time," interim manager Tom Lawless said. "He's made some adjustments in his swing. He's a hard person to defend because he can drop a bunt down or he can rip it right pass the third baseman or he's got power also ... I think he's going to be a fun young man to watch in the future."
Marisnick, who has also wowed coaches with his excellent play in the outfield, attributed his recent success to extra work he's done in the batting cage.
"I'm just getting a little more comfortable out there and putting good swings on good pitches," he said.
Houston took two of three from the Mariners, who entered the day a half-game back for the second AL wild card.
Rookie Collin McHugh (11-9) allowed four hits and three runs in six innings to extend his career-best winning streak to seven. He's the first Astros pitcher to win seven straight since Roy Oswalt reeled off nine in a row from Aug. 23, 2006, to April 17, 2007.
The Astros trailed 3-1 in the fifth inning before an RBI double by Jose Altuve. A two-run single by Presley, who finished with three hits, came with two outs in the inning to make it 4-3 and chase Hisashi Iwakuma (14-9).
Michael Saunders hit a two-run homer for the Mariners, who were outhit 14 to seven.
Iwakuma was trying to bounce back from his last two starts where he was 0-2 with a 12.91 ERA. Instead, he allowed six hits and four runs in 4 1/3 innings for yet another loss.
Houston was still up by one in the seventh when Marisnick padded the lead with his homer to the Crawford Boxes that made it 7-3. Two of Marisnick's three homers this season have come in the last two games.
Altuve, who leads the majors with a .345 average, went 2 for 4 to give him 220 hits this season. That's the most hits by a second baseman since Charlie Gehringer had 227 in 1936 for the Detroit Tigers. He was lifted from the game with two outs in the top of the ninth inning and received a standing ovation from the crowd in Houston's final home game of the season.
"He's the catalyst of the ballclub," Lawless said. "When he gets on things happen. He's got ... 220 hits and that's really unheard of."
Houston rookie first baseman Jon Singleton turned an unassisted double play for the first two outs of the eighth inning. He caught a liner hit by Austin Jackson before tagging Miller at first base for the second out.
Mariners: LF Dustin Ackley, who hit two homers in Friday's 10-5 win, returned to the lineup after missing Saturday's game with an ankle injury.
Mariners: Left-hander James Paxton will pitch the opener of a four-game series at Toronto. Paxton, a Canadian who'll be making his first career start against the Blue Jays, is 2-2 with a 2.39 ERA in his last four starts.