The right-hander allowed one run in seven innings Sunday, helping the Mets salvage the finale of their three-game series against the Florida Marlins with a 7-1 victory.
Despite winning just twice in their past eight games, the Mets are only 2½ games behind NL wild-card leader Philadelphia, which lost to Washington.
"This game was very important to my team," Seo said through a translator, "because this was a game that could start us off to the playoffs."
The Mets improved to 1-2 on a 10-game trip.
"That's why you don't panic. That's why you don't overreact," manager Willie Randolph said. "We know very well that things can change at the drop of a dime, so we'll just keep playing."
New York begins a three-game series Monday against NL East leader Atlanta.
Florida missed a chance to overtake the Phillies and remained a half-game back. The Marlins play their next 11 games on the road against fellow wild-card contenders, starting Monday at Washington.
"We're playing all the teams that are right there with us," center fielder Juan Pierre said. "You can handle your business and control your destiny. That's what you want to do in September. This is the road trip to do that."
The Marlins could do little against Seo (7-1), who allowed only five hits. He improved to 5-0 with a 1.70 ERA since being recalled from Triple-A Norfolk on Aug. 6.
"He has been outstanding," teammate Cliff Floyd said. "He has given us an opportunity every time he has stepped on the field."
Floyd hit a two-run homer against A.J. Burnett (12-9), who consistently threw 96 or 97 mph but still lost his third consecutive start. He struck out nine but allowed eight hits -- five for extra bases -- before departing down 5-1.
Burnett and Josh Beckett, both vital to the Marlins' push for a playoff berth, are a combined 0-5 in their past six starts.
"We've got to get Beckett and Burnett to come through for us to give us an opportunity," manager Jack McKeon said.
For the second consecutive start, Burnett left without talking to reporters.
Floyd hit his 29th homer of the year and second in two games with two outs in the third. Kaz Matsui went 3-for-5 and scored three times, and David Wright and Carlos Beltran each drove in two runs for the Mets, who scored five runs with two outs.
Burnett struck out Jose Reyes with a 97 mph fastball to start the game, but Matsui turned on a 96 mph pitch and tripled. He came home on Beltran's groundout.
"Like the old saying goes -- the harder it goes in, the harder it goes out," McKeon said.
Beltran reached on an infield single with two outs in the third, taking advantage of shortstop Alex Gonzalez's sore elbow to beat a weak throw. Floyd then homered to center field for a 4-0 lead.
Florida scored in the third when Juan Encarnacion doubled and came home on a two-out wild pitch, only the second of the year by Seo. He twice pitched out of two-on, two-out jams.
"He didn't give in to us," Pierre said. "He pitched backwards -- when we thought he was throwing the fastball, he would throw the changeup, and when we thought he was throwing the changeup, he would throw the fastball. He mixed it up well. He got a lead, and offensively we couldn't get anything going."
- Burnett fell to 2-6 lifetime against the Mets.
- Reyes went hitless in three at-bats against Burnett and is 0-for-13 lifetime against the right-hander.
- RHP Jim Mecir, returning from a bout with right shoulder tendinitis, pitched for the first time since Aug. 6 and retired the Mets in order in the eighth.