"To come in here against a team like New Jersey, that plays so consistently good and are so big and strong, to win like that, we really needed that," said Anderson, the Thrashers' coach. "I now know that there is a pulse in our room, that they do care. I appreciate that."
It was the Thrashers' first shutout of the season. For Lehtonen, it was his 12th career shutout and first against the Devils.
Kovalchuk, added Thursday to the Eastern Conference team for the NHL All-Star game, lived up to the billing with key contributions in Atlanta's three-goal second period.
"It's always nice to get a win," Kovalchuk said. "Hopefully in the second half of the season we will get way more points than we did in the first half. This was a total team effort. Guys were fighting to finish checks, and Kari gave us a hell of a game."
Lehtonen also had a star turn to preserve the win, coming up with a big pad stop on Brian Rolston's breakaway bid in the scoreless first period.
New Jersey, which had won five of the previous six games against Atlanta, suffered its fourth shutout of the season, all at home.
Armstrong opened the scoring at 3:03 of the second, chipping a shot into the slot that dribbled through Devils goalie Scott Clemmensen.
Kovalchuk upped the lead to 2-0 with a power-play blast from the high slot at 5:31. He later nudged the puck ahead to create the 2-on-1 break for Slater and Chris Thorburn that Slater polished off at the 14-minute mark.
Clemmensen, making his 13th straight start for the Devils, was yanked after allowing three goals on 19 shots through two periods.
"It was a coach's decision," Clemmensen said about the benching. "The way the game was going at that point, there was very little room for argument."
Kevin Weekes took over in the third, and was victimized on the first shot he faced when Reasoner made it 4-0 at 2:09.
Devils coach Brent Sutter was at a loss to find a single positive, admitting it was New Jersey's poorest effort of the season.
"You guys saw it as well I did," Sutter said. "I feel bad for anybody who had to come and watch that."
The Devils head out on a six-game trip that starts in Los Angeles against the Kings on Saturday. They return on Jan. 21 to host Montreal before playing two more on the road in Ottawa and Boston. ... Devils D Colin White returned after missing five games with an upper-body injury. With White back, the Devils scratched Jay Leach. ... Each team had a forward named Thursday as a reserve for the All-Star game: Kovalchuk for the Thrashers and Zach Parise for the Devils. ... C Bryan Little, the Thrashers' leading goal scorer with 19, missed his second straight game because of a rib injury.
Copyright by STATS LLC and The Associated Press
Arena: Prudential Center Location: Newark, New Jersey
Referees: Paul Devorski, Fred L'Ecuyer Linesmen: Pierre Champoux, Steve Miller
Attendance: 16,489 (93.6% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
No scoring this period
Colby Armstrong (11)
Assist: Todd White
Ilya Kovalchuk (15)
(Power Play) Assists: Slava Kozlov, Todd White
Jim Slater (4)
Assists: Chris Thorburn, Ilya Kovalchuk
Marty Reasoner (7)
Assists: Ron Hainsey, Joey Crabb