Hisanori Takahashi, who pitched a scoreless eighth inning in Tuesday's 1-0 win, was called upon to start the eighth on Wednesday, but after retiring the first two hitters, he gave up a single to Todd Helton and walked Carlos Gonzalez, both left-handed hitters.
"We thought that once we got to a certain point, we would find that [eighth-inning guy], but we've yet to solve that, to be honest with you," manager Jerry Manuel said. "We're trying to mix and match, trying to use who we think is the best possible matchup for us, and it just hasn't worked out for us."
The late dramatics spoiled a fine outing for Niese, who scattered five hits over seven innings and did not allow a runner to reach scoring position until the seventh. After Troy Tulowitzki and Mora opened that inning with consecutive singles, Niese induced a groundout and a sacrifice fly before getting Clint Barmes to pop up and end the Rockies' first real threat of the game.
The rookie left-hander struck out seven and walked none.
Manuel said that Niese was asked if he could go back out to pitch the eighth inning, but the 23-year-old told the coaching staff that his hamstring, which put him on the disabled list earlier in the year, was beginning to tighten up. As a result, Manuel decided not to send Niese back out for fear of further injury.
Niese, however, said that he didn't tell the coaching staff about the hamstring until after they told him that he was done.
"I don't think that had any factor in being taken out," Niese said.
A lack of offensive support forced the bullpen to be perfect once again, as two first-inning runs were all the Mets could muster. The team has been held to three runs or fewer in seven of its nine games this month.
"It's a lot of pressure to ask your starting pitching and bullpen to hold a one-run lead every game," said David Wright, who went 0-for-4 with four strikeouts.
After Jose Reyes led off the game with a bunt single against Rockies starter Jeff Francis, Angel Pagan drilled his 10th home run of the season into the left-field seats.
But the Mets could do nothing more against Francis, who held them to three hits and a walk in six innings.
"We came out of the break, and even before we went into the break, we didn't do much offensively," Manuel said. "If you don't do that when you do get a lead, you have to expect to hold it, so you would need some strength down in the bullpen. For the most part, it's been a struggle for us."
The last time the Mets (56-57) won two straight games, they were coming off a season-high eight-game winning streak, sitting just a half-game out of first place. Wednesday's loss moved them 9 1/2 games out of first and forfeited Wild Card position to the Rockies (59-54), another team with postseason hopes.
"Melvin hitting a grand slam is as big as it gets," Helton said. "I don't know if you call it a must-win game, but it was big."