MIAMI - After managing the emotional swings of a season-altering homestand, after turning Citi Field into an open-air revival, after sweeping their top rivals before delirious crowds, the Mets finally stand alone.

They did it emphatically, of course, as has been their style of late. With their 12-1 rout of the Marlins Monday night, the Mets displaced the Nationals for control of the National League East.

"They've earned it. They belong there," said manager Terry Collins, whose team showed no signs of a letdown. "And hopefully we stay there for a while."

Yoenis Cespedes staged a one-man exhibition, tying a franchise record with three doubles, part of a four-RBI onslaught in which he just missed a pair of homers.

Rookie Michael Conforto, 22, hit his first big-league homer, a three-run shot in the second inning that ignited the Mets. And Bartolo Colon, 42, allowed one run in eight innings for his first victory since June 12.

Those flourishes only added to the ultimate takeaway. The Mets started the night in a virtual tie for first place, percentage points behind Washington. But with the Nationals losing to the visiting Diamondbacks, 6-4, the Mets obliterated any lingering ambiguity about the standings, taking a one-game lead.

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The Mets, winners of four straight, have not led the division this late in a season since their last full-fledged pennant race in 2008.

"We've been talking among all the players, not only the veteran guys," Colon said through a translator. "From now on, every game is important. Every game counts. We've got to take every game like it's the last."

On July 4, the Mets were 41/2 games behind the Nats. Now, a month later, the new-look Mets have retaken the driver's seat.

The Mets spent the days leading up to last Friday's trade deadline trying to infuse life into the National League's least productive offense. They did it by trading for Kelly Johnson and Juan Uribe. They did it by promoting Conforto. They did it by beating the trade deadline to acquire a bona fide star in Cespedes.

That newfound depth shined through Monday night, and Stony Brook product Tom Koehler stood little chance. The Mets pummeled him for seven runs (six earned) in 4 1/3 innings and swelled his ERA against them to 14.73 in three starts this season.

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By the time Koehler was chased in the fifth, he already had served up a lasting memory. It belonged to Conforto, whose first big-league homer jumped off his bat at 112 mph, according to MLB.com.

"It's the best feeling in the world," said Conforto, who was demoted Saturday and promoted Sunday when Kirk Nieuwenhuis went to the disabled list.

The bench serenaded Conforto as he made his first home run trot. "They were rowdy," he said. "That was pretty cool. It was just a blur. The whole trip around the bases was just a flash in the mind."

The drive sparked the Mets, who enjoyed a bounce-back outing by Colon (10-10, 4.72). The righthander had been 0-6 with a 6.16 ERA in seven starts since June 12. But he looked transformed while pitching the Mets back to first place.

"Everybody goes through down times," Collins said. "We went through ours. We held together. And we're back."