NEW YORK -- The San Diego Padres, the team with the worst run differential in baseball, enjoyed their best win of the season Wednesday night.

It's a sign of how fast things have unraveled for the New York Mets -- preseason World Series contenders -- that Wednesday night's loss might not be their worst of the year.

Hunter Renfroe hit a tiebreaking homer leading off the eighth inning to cap a four-run comeback by the Padres, who survived a hectic ninth to escape with a 6-5 win over the Mets at Citi Field.

The four-run comeback tied the biggest of the season for the Padres (17-31), who began the day with the worst record in baseball but moved past the Philadelphia Phillies by virtue of the latter's loss to the Colorado Rockies.

San Diego, which has won just two of its last eight games and has been outscored by 90 runs this season, came back from a 4-0 deficit to beat the Arizona Diamondbacks on April 26.

"It's a great fight-back (win) for the guys," Padres manager Andy Green said. "It's necessary to come fight back sometimes. I think our guys, for where we're at right now, record(-wise), in the standings, our guys fight. They do. They're relentless."

The Mets cruised to a 9-3 win in Tuesday's series opener and appeared headed for another easy victory over the rebuilding Padres after they chased San Diego starter Jarred Cosart in the third and carried a 5-1 lead into the fifth.

But the Padres, who had two Rule 5 draftees in the lineup, closed within 5-3 against Mets starter Robert Gsellman in the fifth before completing the comeback against four relievers in the seventh and eighth.

Mets right-hander Fernando Salas retired the first two batters he faced in the seventh before loading the bases. Neil Ramirez entered and gave up a long two-run single to Wil Myers, who missed a grand slam by a few feet when his ball bounced off the center-field wall.

Josh Edgin got the final out of the seventh before Renfroe greeted Josh Smoker (0-2) with a home run deep into the second deck in left.

Green and the rest of the Padres endured some nail-biting moments. Left-hander Brad Hand, pitching in a ninth-inning save situation for the first time this season, loaded the bases with none out via two singles and a walk.

But Hand struck out Curtis Granderson and Rene Rivera before retiring Juan Lagares on a flyout to right to post the third save of his career.

"Probably one of the more exciting (wins), for sure, the way it ended," Renfroe said.

Ryan Buchter (3-2), the fourth of six Padres pitchers, picked up the win with a scoreless seventh. The five San Diego relievers combined to allow one run and four hits in 6 1/3 innings.

"You can't say enough about our bullpen keeping us in the game all game," Myers said.

A struggling bullpen is a big reason the Mets (19-25) have lost nine of 12. New York relievers are 7-11 with a 5.08 this season and have twice blown leads of at least four runs in the last 10 days.

The Milwaukee Brewers came back from a six-run deficit in an 11-9 win on May 14.

"You've got to make decisions with what you have -- you take the best you've got at those times," Mets manager Terry Collins said.

The Mets aren't being helped much either by their starters, who have combined to post a 5.13 ERA.

Gsellman, who allowed three runs, six hits and one walk while striking out three in six innings of his first start since May 13, became the 21st starter in the last 22 games to fail to pitch beyond the sixth inning.

"This kid has really been struggling," Collins said of Gsellman, who has a 6.45 ERA. "You want him to leave with a good feeling. He gave us six good innings."

Yangervis Solarte collected the Padres' first three RBIs with a third-inning single and a fifth-inning, two-run double. Myers and the Rule 5 players, Allen Cordoba and Luis Torrens, each had two hits apiece.

Cosart gave up four runs, four hits and four walks while striking out one in 2 2/3 innings.

The Mets scored four runs in the third, when Wilmer Flores hit a three-run double and Curtis Granderson followed with an RBI single. Michael Conforto added an RBI single in the fourth.

Flores, Conforto and Neil Walker all had two hits apiece.

NOTES: The Mets activated C Travis d'Arnaud from the 10-day disabled list and placed LHP Tommy Milone (sprained left knee) on the 10-day disabled list, retroactive to Monday. ... The Padres will promote RHP Dinelson Lamet from Triple-A El Paso to start Thursday's series finale. It will be the major league debut for Lamet, who was at Citi Field on Wednesday.