ATLANTA - Almost everything about the Mets' sloppy win Sunday smelled of a mundane afternoon in the Grapefruit League.

From the avalanche of silly mistakes to a seeming lack of urgency stemming from the Nationals' steep descent, the Mets appeared to treat their series finale against the Braves as a cursory walk-through. They had no business winning.

Yet here they were, rejoicing in a 10-7, 10-inning victory, far from their prettiest of the season and perhaps their most absurd.

"It's really been incredible," said manager Terry Collins, who watched his team nearly flatline before roaring back to life.

Trailing 7-4, the Mets were down to their last out in the ninth, and Juan Lagares was down to his last strike. But Lagares lashed a double and Curtis Granderson walked to set the stage for Daniel Murphy.

"I didn't think I would hit a homer," said Murphy, whose three-run shot tied it. "But I was trying to."

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The Mets pushed ahead with three in the 10th. The winning run, appropriately, came on a brutal lapse by the Braves after the Mets had spent the day tripping over their own feet.

With runners at the corners and two outs, Kevin Plawecki appeared to hit into an inning-ending forceout, but third baseman Adonis Garcia threw wide of second, just enough to pull Daniel Castro's foot off the bag.

Kirk Nieuwenhuis scored, his reward for triggering the rally with a two-out walk against Edwin Jackson. The Mets scored twice more on bases-loaded walks by Jackson and Danny Burawa to complete a meltdown by the Braves' bullpen.

"Everybody right now is doing an unbelievable job," said Lagares, who spoiled a pair of two-strike pitches before he jumped on a slider to trigger the ninth-inning rally.

If any team had license for a letdown, it was the Mets. For all the ways that they've rollicked through the most critical stretch of their season, a speed bump was inevitable. Instead, they extended their winning streak to seven games and kept their NL East lead at 91/2 games.

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At 82-61, they have clinched their first winning season since 2008. They concluded a 10-game road trip with an 8-2 record. Not since 1989 had the Mets swept the Braves in a four-game series. Not since 1985 had they done so in Atlanta.

"It's really hard to imagine that we would be sitting where we are right now, even though we knew we thought we had a good team," Collins said. "This is far and above what we expected."

The Mets rested nearly half their starting lineup and worked with only a skeleton crew in the bullpen. Still, Jonathon Niese kept the damage to three runs (two earned) in six innings, picking up his defense.

First baseman Lucas Duda took his foot of the bag while fielding a throw, then let a foul pop fall to the ground. Murphy whiffed on what should have been a sure double play, Granderson lost a ball in the sun and Juan Uribe let a ground ball bounce through his legs.

Tim Stauffer, the veteran reliever making his Mets debut, allowed the tying run to score when he opted for a double play when he could have had a clear play at the plate. Each gaffe cost the Mets runs, helping them to squander leads of 2-0 and 4-3. Yet they prevailed, with two of their most forgotten men in the center of it all.

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Bobby Parnell, the former closer exiled to the fringes of the roster, tossed 1 1/3 scoreless innings of relief for the win. And reigning Gold Glover Lagares, his role diminished with Yoenis Cespedes now patrolling center, delivered the at-bat that brought the Mets back to life.

"I just felt happy. That's a great comeback, you know?" said Lagares, who jogged the last 20 feet with his fist in the air on Murphy's homer. "Ninth inning, two down . . . that was great."