SAN FRANCISCO — Lately, the Mets have offered little in the way of relief. Though the bullpen has been a strength for much of the season, their recent downturn has mirrored that of the team overall.

Entering Sunday night’s series finale against the Giants — a 2-0 Mets victory in which Noah Syndergaard pitched eight innings and Jeurys Familia earned his 41st save — the Mets’ bullpen had posted a 6.13 ERA in August, a jump from the 2.58 mark it had in July.

The issues, manager Terry Collins said, stem partly from the Mets’ recent problems with the rotation.

“With all the different things we’ve had to do, with some of the turmoil we’ve had in the starting rotation, the spot starts where you’re not sure what you’re going to get, we’ve taxed our bullpen,” Collins said. “The back end for sure. Those guys have been in 60 games apiece. I think you’re starting to see a little fatigue.”

Indeed, there has been a trickle-down effect on the bullpen, which entered Sunday night with a 9.02 ERA as a group in 10 games since Aug. 11.

For instance, Steven Matz missed his scheduled start Friday with shoulder soreness. He’s set to be examined Monday, leaving his next start Thursday up in the air. The Mets will play short as they sort out Matz’s situation, with Seth Lugo making Matz’s starts when necessary, though that means he’s not available as a long man out of the bullpen.

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Further complicating matters, Jonathon Niese wound up in the rotation after Logan Verrett failed to hold down the fifth spot. Syndergaard has dealt with elevated pitch counts in the second half and Jacob deGrom is coming off his worst start of the year.

Those issues have forced the bullpen to work more innings at a time when it has struggled.

Hansel Robles has allowed 13 runs in his last 9 1⁄3 innings dating to Aug. 1 after allowing only three in his previous 21 innings. Collins wonders if he has been overthrowing, perhaps a side effect of fatigue.

“He’s gotten away from what really made him successful a couple of weeks ago, which is to pound the strike zone,” Collins said. “Right now, he’s falling behind in the count and getting himself in trouble.”

Righthander Erik Goeddel had lowered his ERA to 2.70 before surrendering five runs in 1 1⁄3 innings in his next three outings. He paid for that downturn with a demotion to Triple-A Las Vegas on Sunday.

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Lefty specialist Jerry Blevins logged 1 1⁄3 scoreless innings Thursday, then allowed a pair of inherited runners to score Friday. On Saturday, Collins said he was unavailable with left forearm tightness.

Blevins said the tightness was normal, given his recent workload, and that Saturday’s day off was scheduled. Nevertheless, Collins could not say with certainty if Blevins would be available in the series finale. As it turned out, he wasn’t needed.

During the weekend, the Mets brought in fresh arms by promoting lefty Josh Smoker and activating righty Jim Henderson off the disabled list after a stint of more than two months.

Smoker allowed two runs in his big-league debut Friday but bounced back to throw two-thirds of a scoreless inning Saturday. Henderson has yet to appear.

“Bullpens are extremely important today, very important, so much more than they had been years ago,” Collins said. “When teams win, you build your bullpen.”