SAN DIEGO -- Justin Dunn did his part on Sunday, pitching on short rest in the construction of the Mariners’ six-man rotation. He limited the Padres to just one hit, albeit a big one, and worked his way out of a major jam in the fifth inning. But a beleaguered Seattle bullpen and a lack of offensive traction against Yu Darvish wound up costing the Mariners in a 9-2 loss at Petco Park that completed a three-game sweep.

Given the context of the opponent, the shorter leash he was on and the state of the Mariners’ pitching staff -- having lost Kendall Graveman to the injured list on Sunday -- it was arguably Dunn’s best start of the season. He wound up throwing 71 pitches over five innings, and the only run he gave up was on a towering, 441-foot homer from Fernando Tatis Jr. to lead off the second.

Dunn also helped himself out at the plate, accounting for his lone run of support by muscling a game-tying, two-out RBI double in the fifth off Darvish, who overcame seven hits and went seven strong innings. It marked Dunn’s first career hit and RBI. Dating all the way back to his days at Boston College, Dunn had just two career hits entering Sunday, both in 2018 for Double-A Binghamton when he was in the Mets organization.

“To be able to get a hit in the big leagues, especially off a pitcher of that caliber, was a pretty cool moment,” Dunn said.

Above all, Dunn showed much stronger command than ever before this season. He walked three, but two of those came in stingy at-bats in which he reached a full count. The first was to Tatis in their next encounter following the homer in the fourth, and his second came after a 10-pitch battle with Wil Myers to lead off the fifth, which featured five foul balls. The third came on four pitches to Ha-Seong Kim, which put him in a big jam with runners on second and third after a Darvish grounder, but Dunn was able to escape by punching out Tommy Pham to end the inning and his day.

Because of the high-intensity pitches in those sequences, the moderate fatigue he battled after legging out the double and the fact that the Padres were sending their Nos. 2-4 hitters up in the sixth for what would’ve been the third time through, manager Scott Servais had a pretty easy decision not to send the right-hander back out.

“Hitting took a lot out of my legs for sure, running and standing out on the bases,” Dunn said. “That's what took a lot out of my legs. I definitely was fatigued. In that situation coming up, and with 2-3-4 [hitters], I could have went either way. But no, I was definitely tired.”

Dunn was “gung-ho” about starting on one day's shorter rest than he’s accustomed to and admitted that he probably wouldn’t have been up for the challenge as recently as a year ago. He’s hoping that it’s the first of a few in his career.

“I was excited because there's going to be a point when we really get rolling, where, hopefully, I'm in a situation to do that in a playoff run,” Dunn said. “And today was just a good test to show me I'm able to do it. I’ll file that one away in the routine and know what I have to do to be ready to pitch [every] five days. … I was able to get deeper, honestly, than I thought I was going to be able to.”

But after Dunn departed, the Mariners had an uphill climb from there.

Anthony Misiewicz came on in the sixth, faced just four batters, gave up three runs and failed to record an out. Then in the seventh, Robert Dugger worked his way into a bases-loaded jam before surrendering a mammoth, 447-foot grand slam to Tatis that put the game out of reach. It was the first outing for each after returning from the IL for COVID-related issues the day prior. Wyatt Mills, who took Graveman’s roster spot, hit his first batter in the eighth and then gave up an RBI triple to Kim.

“Unfortunately, a rough day for Misz. He comes in there in the sixth inning, and he’s struggled here of late, and I thought that was a good pocket for him,” Servais said. “It just didn't work out. And after that, the game got away from us. But again, Justin Dunn -- can't say enough about the effort and the job he did today.”