PHOENIX - Bartolo Colon had been tossing a gem Saturday night, in position for what would have been his ninth victory, the most in the major leagues.

He operated with only a one-run cushion, all that a depleted Mets lineup could muster on his behalf. Until the seventh, he had made it work. But with one transgression, the slim lead evaporated, and the Mets found themselves careening toward a 2-1 loss to the Diamondbacks.

After a night of pinpoint command, Colon left an 85-mph fastball belt high and over the heart of the plate. Welington Castillo, who entered play hitting .149 for his third big-league team in the last month, responded by smashing a two-run homer.

"You can't make those mistakes in the big leagues," Colon said through a translator. "You're going to pay for them."

That has proved especially true for Mets pitchers, who have received little help from a lineup besieged by injuries.

"It's been happening a lot . . . You've just got to work through it," Terry Collins said after the Mets scored only once despite 10 hits.

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The Mets rallied in the ninth, putting the tying run in scoring position with the help of catcher's interference, but John Mayberry Jr. hit into a game-ending double play.

The Mets (30-27) dipped a half-game behind the NL East-leading Nationals.

Juan Lagares hit his first homer in almost a month, skimming a drive off the top of the rightfield fence in the second for a 1-0 lead. But for the second straight night, the Mets loaded the bases in a critical spot and came away with nothing, this time when Eric Campbell lifted a harmless fly ball to end the sixth.

Colon held Arizona to two runs in seven innings, a breakthrough after posting a 7.31 ERA in his previous five starts. He also had his fourth hit, extending his unlikely hitting streak to three games.

But all he got for his trouble was his fourth loss, leaving Collins to sound a familiar refrain. "He pitched his heart out tonight," he said. "And we can't get him any runs."