NEW YORK -- The Oakland Athletics lost two games this weekend in New York. But they also found an eighth-inning reliever and, on Sunday, earned a win when a young player found redemption for an earlier mistake.

Such is the path of progress for one of the handful of teams in the major leagues committed to rebuilding at the trade deadline.

Matt Chapman atoned for a baserunning blunder by hitting the tie-breaking solo homer in the seventh inning as the Athletics edged the New York Mets 3-2 at Citi Field.

"It's definitely nice to make up for what you feel like is a pretty crucial error," said Chapman, who was one of four rookies in the A's starting lineup Sunday. "I was glad that I got to make up for that run that we missed out on."

Chapman appeared as if he might wear the goat horns in the fifth inning, when he led off with a double and took third on a wild pitch by Mets starter Rafael Montero.

But Chapman, who was preparing to take off on contact if eighth-place hitter and fellow rookie Jaycob Brugman put the ball in play, was caught leaning too far toward home on a check swing by Brugman two pitches later. New York catcher Rene Rivera fired to third and easily nabbed Chapman.

"With (pitcher Daniel) 'Goose' (Gossett) up next, we're going to have to do the best we can to try and score on the play," Athletics manager Bob Melvin said. "When the ball crosses, you have to get back, but Brugman looked like he was swinging at it, so I don't know that I can say 100 percent that was a complete baserunning mistake."

Brugman followed with a single that would have easily scored Chapman. Instead, Oakland didn't add on to its lead in the fifth and the Mets tied the game in the sixth on an RBI groundout by Jose Reyes.

Chapman wasted little time making up for the mistake in his next at-bat, when he launched a 2-0 pitch by Montero deep into the left field seats for his second homer in as many games and his fourth in 68 at-bats since being recalled from Triple-A Nashville June 15.

"For (being at) the big-league level for the first time, there's going to be some struggles," Melvin said. "But he's always one swing away from putting the ball in the seats."

Chapman's homer put fellow rookie Gossett (2-5) in line for the win. Gossett allowed two runs, five hits and two walks while striking out six in six innings.

Daniel Coulombe, Blake Treinen and Santiago Casilla preserved the lead for the Athletics, who squandered leads in losing the first two games of the series. Coulombe and Treinen each tossed a perfect inning before Casilla worked around a hit in the ninth to earn his 16th save.

Treinen, who was acquired from the Washington Nationals July 16 in the deal that sent set-up men Sean Doolittle and Ryan Madson to the Nationals, allowed a run in two-thirds of an inning Friday but retired all seven batters he faced in the final two games.

"I think that eighth inning is a nice spot for him, if we get there," Melvin said of Treinen. "Before Casilla, I think he's kind of that guy for us."

Marcus Semien (first inning) and Khris Davis (fourth inning) each hit solo homers for the Athletics and finished with two hits apiece.

Michael Conforto had two hits, including a third-inning solo homer, for the Mets (44-50), who had their four-game winning streak snapped. Jay Bruce singled and eventually scored the second run for New York, which entered Sunday 10 games behind in the National League wild-card race and is likely to be a seller at the July 31 trade deadline.

"We know the situations we're in," Bruce said. "We've played better baseball of late, but I'm not really able to say whether that's going to be enough or not."

Montero (1-7) allowed three runs, seven hits and one walk while striking out four in a season-high seven innings. He also had his first hit in 29 big league at-bats by singling to right-center field in the fifth.

"Just how today went, at least that part really made me happy," Montero said through a translator.

NOTES: The first pitch was delayed 61 minutes by rain. ... Both teams had unusual moments on the basepaths. Mets RHP Rafael Montero went from first to third on a wild pitch immediately following his single in the fifth. In the ninth, Athletics 2B Jed Lowrie broke from first, believing OF Rajai Davis was trying to steal third. But Davis was bluffing and went back to second, where Lowrie stood until he was tagged out by Mets C Rene Rivera for the rare "catcher unassisted" caught stealing. ... The Mets' top prospect, Triple-A Las Vegas SS Amed Rosario, was hospitalized Saturday with a stomach issue. ... Athletics RHP Jharel Cotton (thumb blister) will make a second rehab start for Triple-A Nashville on Monday.