SEATTLE -- Jose Altuve had four hits and three RBIs and teammate Carlos Gomez added his second career grand slam as the Houston Astros hammered the Seattle Mariners 8-1 on Sunday.

Altuve had hits in each of his first four at-bats while serving as the designated hitter. After a first-inning single, Altuve gave Houston a 3-0 lead with his 15th home run of the season, a two-run shot in the third. Altuve added an RBI single in the fifth, putting the Astros ahead 4-0.

Gomez's seventh-inning grand slam opened an 8-0 lead.

Houston starter Collin McHugh tossed six scoreless innings despite loading the bases twice. He allowed four hits and four walks while striking out 10. McHugh (6-6) beat the Mariners for the third time this season.

Seattle (46-46) left 10 runners on base and committed four errors. The Mariners also hit into five double plays.

The Mariners had a chance to take control in both the first and third innings, during which they loaded the bases with fewer than two outs, but Seattle came up empty on both occasions.

McHugh loaded the bases with two one-out walks and a hit-by-pitch in the first, then he got a strikeout and a groundout to get out of that jam. Two innings later, the Mariners loaded the bases with no outs but couldn't capitalize after another strikeout and an inning-ending double play.

Seattle third baseman Kyle Seager struck out in both innings, stranding six runners on base in the process. He also had two errors, giving Seager 12 this season and eight since June 2.

The Mariners had three errors in the first two innings, and that didn't even include a routine fly ball that left fielder Seth Smith lost in the sun and had bounce off his glove for what was ruled a double.

Seattle starter Mike Montgomery (3-4) allowed four runs (three earned) off seven hits in five innings. Reliever Nathan Karns, a former starter, served up the grand slam in the seventh.

The Mariners' only run came on a two-out RBI single from Seager in the eighth. That cut the Houston lead to 8-1.

Houston (50-42) stayed within 4 1/2 games of first-place Texas in the American League West standings. The Astros have gone 33-14 since May 23, the best record in baseball.

Altuve went 4-for-5 to bring his AL-leading average up to .346. Gomez went 1-for-5 with his fifth home run of the season, and teammate Marwin Gonzalez added two doubles and scored three times.

NOTES: Seattle SS Ketel Marte (minor ankle sprain) and RF Nelson Cruz (bruised foot) were back in the lineup Sunday. Both players sat out Saturday's game. ... Seattle LF Seth Smith was in the leadoff spot for the first time this season on Sunday. ... Astros 2B Jose Altuve served as DH for the sixth time this season. ... Houston starter Collin McHugh had a 2-0 record and 2.25 ERA against Seattle heading into Sunday's game. Against the rest of the league, McHugh was 3-6 with a 4.80 ERA. ... The Mariners officially named RHP Felix Hernandez as the probable starter for Wednesday's game against the Chicago White Sox. Hernandez is on the 15-day disabled list and hasn't pitched in a major-league game since May 27 due to a strained calf. ... The Astros introduced Cuban 3B Yulieski Gourriel over the weekend, saying they expect him to play with them at some point this season. Gourriel, a 32-year-old star who was playing in Japan, is expected to play a few games at Double-A Corpus Christi before joining the Astros at some point. "One of the reasons (we) worked so hard to get this deal done as timely as we could," general manager Jeff Luhnow said, "is I want -- and Yuli wants -- him to be part of a playoff run this year." ... Sunday wrapped up the three-game series and marked the final time that the Mariners and Astros will play against each other until mid-September. Seattle hosts the Chicago White Sox in a three-game series that begins Monday, while Houston heads to Oakland for a three-game series with the Athletics.