Texas had a season-high 18 hits, the most by the team since Sept. 8, 2019. The Rangers matched their longest winning streak of the season with their fourth straight. Seven players had multiple hits, including three with three each.
"The at-bat quality was just phenomenal today," Rangers manager Chris Woodward said. "Even when we got the big lead, I felt like we could have scored a bunch more."
Semien played with Oakland from 2015-2020 and was an All-Star last season with Toronto before signing with Texas for seven years and $175 million. The 31-year-old had not homered since October before crushing an 0-1 pitch from Jake Lemoine over the wall in center field for his sixth career grand slam and fourth at the Coliseum. Semien also drew a bases-loaded walk in the sixth.
"When I hit it I was like, 'It's probably going to get caught,'" said Semien, who last year set an MLB record for second basemen with 45 home runs. "Sometimes day games, you hit it right here and it carries. Of course, a grand slam is great. First home run with a new team was a grand slam, a swing to help us win. I'll take it."
Semien became the first player in major league history to hit 40-plus home runs in one season and then have a 40-plus game homer drought the following season, according to STATS.
"He's been swinging the bat well, getting hits, getting on base, doing a lot of thing for us," Woodward said. "That was a big hit because that put us ahead 9-1. We needed that. We needed a little bit of breathing room."
The Rangers won handily after taking the first two games of the series in their final at-bat. Texas took advantage of an overwhelmed A's bullpen after knocking Zach Logue out of the game in the third inning.
Seager finished with three hits and two RBI. Kole Calhoun and Andy Ibañez also had three hits.
"We all know our ability in this room," Semien said. "The results may not have showed that in the first month or whatever but in terms of talent, work ethic and ability we have a good group."
Ramón Laureano hit his first home run for Oakland, a solo drive off Taylor Hearn. The A's, who were managed by bench coach Brad Ausmus while Mark Kotsay attended his daughter's graduation in San Diego, have lost 10 of 14.
Hearn (3-3) allowed three runs, two earned, in six innings. The Rangers left-hander had five strikeouts and one walk.
The Rangers are 5-1 against the A's this season after going 9-10 in the series last year.
Logue (2-4) left the game after allowing Nathaniel Lowe's RBI triple with two outs in the third. Earlier in the inning, Seager hit his ninth home run and García drove the next pitch to left for his seventh.
"I don't think (Logue) had a real good feel for the baseball the whole time," Ausmus said. "The command kind of came and went."
GRIMM DESIGNATED BY A'S
A's reliever Justin Grimm was designated for assignment. The right-hander had a 4.11 ERA in 15 games this season. RHP Austin Pruitt was selected from Triple-A Las Vegas.
Rangers: 3B coach Tony Beasley was forced out of the game because of a tight Achilles tendon in his right leg.
Athletics: RHP Daulton Jefferies (thoracic outlet syndrome) plans to visit a specialist to get a second opinion next week.
Rangers RHP Phil Dunning (1-3, 4.32) is winless in his last 17 road starts, dating to his tenure with the White Sox. A's RHP James Kaprielian (0-2, 4.50) will make his 27th career start and seventh against Texas.
Ramon Laureano smashes a solo shot to left field
Ramon Laureano unloads a beauty to left field to pull the Athletics closer in the bottom of the fifth inning.