SEATTLE -- A full-fledged pitchers' duel was in swing on Sunday afternoon at T-Mobile Park, as Logan Gilbert and Zack Wheeler battled deep into the matinee in front of a ticketed crowd of 39,588. But ultimately for the Mariners, a lack of run support for their towering ace and a few big homers against their bullpen gave Wheeler the last laugh in a 6-0 loss.

Gilbert surrendered a leadoff homer to Kyle Schwarber on the third pitch of the game, a middle-middle fastball in a 2-0 count, and saw his pitch count balloon in a 15-pitch plate appearance to Nick Castellanos -- the longest in the Majors this season -- that culminated with an inning-ending groundout in the second.

But other than that, Gilbert cruised through six innings, with zero walks, seven strikeouts and only three other hits allowed. He turned heavily to his breaking balls, marking the seventh time this season in which he threw his slider more than any other pitch -- a by-design effort against a team that entered play with a .452 slugging percentage against fastballs, eighth-best in MLB.

“I'm pretty proud of that, honestly, that I can get to that point that we need to do that,” Gilbert said. “And working with the catchers, them knowing me well enough, having trust in me, I have trust in them, where we can go to that and feel like we're not really backed into a corner as much.”

After Gilbert departed, newly acquired reliever JT Chargois worked through a clean seventh -- aided by two impressive catches from center fielder Victor Robles in consecutive at-bats -- before things unraveled in the eighth.

Yimi García, also a Trade Deadline acquisition, gave up a solo homer to Bryson Stott on a center-cut fastball in a full count, and Tayler Saucedo gave up a two-run blast to Bryce Harper and a solo shot to Alec Bohm on consecutive pitches that blew the game open. Mariners manager Scott Servais then turned to Trent Thornton, who allowed another one of Saucedo’s inherited runners to score before finally getting out of the eighth inning.

All the while, Wheeler dominated over a season-high eight frames while surrendering just two hits -- a double to Cal Raleigh in the first and a single to Robles in the third. Raleigh also walked in the third, marking Seattle’s only other baserunner vs. Wheeler.

“He has an elite fastball,” Servais said of Wheeler. “It's much in the same bucket as our young guy, Bryan Woo. It comes out of a different slot. He's able to sink it, ride it, so even though on the radar gun or whatever it may say it's 94-95 [mph] it's playing up to 98-99 mph.”

Wheeler was coming off one of his worst starts of the season, having surrendered seven runs at Yankee Stadium in a 14-4 loss on Monday. But he’s nonetheless been one of the game’s best starters, earning his second All-Star selection.

On Sunday, he lowered his ERA to 2.77, and while the pitching win statistic doesn’t carry as much credibility as it once did, Wheeler picked up his 11th, making him one of just 10 pitchers this year with that many. It’s a number that speaks to his ability to pitch deep into games and preserve a lead for a club that has the best record in the National League.

On the other side, the Mariners continue to struggle lifting Gilbert, who entered the day with the second-lowest run support average in the Majors, at 2.99 runs per outing. Gilbert completed his 18th quality start, which tied him with Baltimore’s Corbin Burnes for the MLB lead, yet the Mariners fell to 11-7 in those outings and are overall 11-12 this year when he pitches.

“I felt good today, for sure, but I mean, it would have been pretty sweet to finish off the series with a win, get the sweep, especially against that team,” Gilbert said.

As for Seattle’s relief corps, even with the reinforcements of García and Chargois, the club has a 5.10 bullpen ERA since the All-Star break, tied for seventh-worst in baseball, after posting a 3.66 ERA in the first half (ninth-best).

The Mariners still won the series and showed significant offensive improvement from its season-long struggles over the first two games. And with Houston and Texas both losing, they also retained sole possession of first place in the American League West heading into Monday’s off-day. Overall, the club has won six of its past nine.