New Jersey got a third-period goal from Mark Fayne. The Devils' eight-game run was tied for the second longest in the NHL this season.
The Devils, 16-2-2 over their past 20 games, dropped 11 points behind Carolina, which is eighth in the Eastern Conference. The Hurricanes beat Pittsburgh 4-1.
"Mathematically, we're still in the hunt," New Jersey center Dainius Zubrus said. "I don't think it's going to change our approach for the next game."
After St. Louis beat Devils goalie Johan Hedberg from the top of the left circle at 2:20 of the second, Gagne made it 2-0 from near the right circle 54 seconds later. Hedberg, making his eighth straight start, had allowed just one goal over his previous three games.
"I think they're a really, really good hockey team," Hedberg said. "They've got a lot of weapons."
The Southeast Division-leading Lightning have a five-point lead -- with one game in hand -- on Washington, which lost 6-0 to the New York Rangers.
St. Louis has three goals and 11 points during an eight-game point streak. Gagne stopped a personal nine-game goal drought.
Hedberg kept the Devils within two goals later in the second by making in-close saves on Teddy Purcell and Stamkos.
"That was a difficult win," Tampa Bay coach Guy Boucher said.
Kovalchuk had an assist to extend his point streak to 12 games (seven goals, 14 points).
Hedberg had won his seven previous starts. He stopped 28 shots.
Roloson finished with 19 saves.
Devils right wing David Clarkson returned to play four shifts in the third after being cut on the right forearm by a skate one period earlier while finishing a check. He estimated the cut required around 18 stitches.
"I didn't want to sit and watch, so I tried to go back and play," Clarkson said. "They said I missed the things [with the cut] that could have been trouble, so it's good. It was lucky."
New Jersey G Martin Brodeur was the backup for the fourth consecutive game since returning from a sprained right knee. ... The California Golden Seals, who went 4-7-1, are the only other NHL team to play 12 consecutive home games. ... Lightning D Mattias Ohlund didn't play because of a lower-body injury. ... Pittsburgh's 12-game winning streak, from Nov. 17 to Dec. 11, is the NHL's longest this season. ... Tampa Bay recalled G Mike Smith from Norfolk of the AHL.
Copyright by STATS LLC and The Associated Press
Arena: Amalie Arena Location: Tampa, Florida
Referees: Paul Devorski, Rob Martell Linesmen: Brian Murphy, Pierre Racicot
Attendance: 19,563 (101.9% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
No scoring this period
Martin St. Louis (23)
Assists: Steve Downie, Steven Stamkos
Simon Gagne (10)
Mark Fayne (4)
Assists: Ilya Kovalchuk, Travis Zajac