ST. LOUIS -- Robert Gsellman's first major league pitch was smacked to the right-center-field wall.

Most of his next 74 turned out a whole lot better.

Making an unexpected debut after starter Jonathon Niese departed four batters into the Tuesday night game, Gsellman worked 3 2/3 scoreless innings and earned the win as the New York Mets stopped the St. Louis Cardinals 7-4 at Busch Stadium.

In becoming the 23rd pitcher in franchise history to win in his big-league debut, Gsellman gave up two hits and three walks while striking out two. He is the first pitcher in Mets annals to toss more than two innings of relief in his first big league win.

"It was my first time ever out of the bullpen," Gsellman said. "It felt awkward. I just tried to make some pitches."

Niese issued two walks and allowed an RBI single to Brandon Moss before leaving with left knee pain. Gsellman was actually up and throwing after Niese's only out, a Stephen Piscotty liner that left fielder Yoenis Cespedes caught at his ankles.

"He reached down to his knee after the second batter," New York manager Terry Collins said of Niese. "Then when we went out there, he said it was killing him. I thought something was wrong when he walked the leadoff hitter."

St. Louis could have been excused if it experienced sympathy pains. In three previous games against Niese, who started the season with Pittsburgh, the Cardinals strafed him for 13 runs on 24 hits over 16 innings.

"That's brutal," center fielder Randal Grichuk said. "I've hit Niese pretty well in the past, I thought I had a good game plan against him, and then I take my first two at-bats off a guy I'd never seen before."

Not that Gsellman gave St. Louis much reason for worry right out of the chute. Yadier Molina rifled his first pitch for an RBI double, and Jhonny Peralta followed with a run-scoring groundout to cap a three-run rally that matched the Mets' output in their half of the first.

However, Gsellman put up three zeros after that, aided by a diving stab by shortstop Asdrubal Cabrera that denied Peralta an RBI single in the third, and he departed with a 6-3 lead.

"I just had to take a couple of deep breaths and slow it down," Gsellman said. "I just had to block it out ... it happened fast."

So did most of New York's scoring against Jaime Garcia (10-9). The lefty hadn't allowed an earned run in 22 1/3 career innings against the Mets at home before Wilmer Flores ripped a three-run homer to left in the first.

Jose Reyes snapped a 3-3 tie in the second with a two-out RBI single and then zipped home on Cabrera's run-scoring double to the wall in right-center. That was a frequent theme -- New York's No. 1 and 2 hitters reaching base continually.

Reyes went 3-for-4 with three runs and an RBI, while Cabrera was 3-for-5 with a run and an RBI.

"Our first two guys were on base seven times," Collins said. "You can't ask for much more than that."

The Cardinals (66-58) didn't lack for chances. They stranded 11 men -- two apiece in the third, fourth, fifth, seventh and eighth innings -- and were 0-for-6 with runners in scoring position after the first inning. Their only run after the first was Grichuk's 16th homer of the year in the sixth off Josh Smoker.

Justin Ruggiano belted a fourth-inning homer for the Mets, and James Loney tacked on insurance with a two-out RBI single in the ninth.

In losing for the first time in four starts, Garcia was touched for seven hits and six runs in four innings, walking one and whiffing six. Despite the result, St. Louis remained 1 1/2 games ahead of the Miami Marlins for the National League's second wild-card spot.

Five relievers picked up the final 15 outs after Gsellman's outing, with Jeurys Familia earning his 42nd save by working a clean ninth inning. New York (63-62) drew within 3 1/2 games of the Cardinals in the wild-card race.

After the game, the Mets said that Niese was headed to the disabled list, to be replaced on the roster by right-handed reliever Erik Goeddel, who will be recalled from Triple-A Las Vegas.

NOTES: St. Louis RHP Lance Lynn (right elbow) will make his third rehab start Wednesday for Double-A Springfield. Lynn pitched twice last week at Class A Palm Beach, but he said it is still just a "slim" chance he makes it back this year. He underwent Tommy John surgery in November. ... New York placed LHP Steven Matz (left shoulder strain) on the 15-day DL and recalled RHP Robert Gsellman from Triple-A Las Vegas. ... The Mets placed 2B Neil Walker on the paternity list and recalled INF T.J. Rivera from Las Vegas.