Carter scored two goals and the Flyers won their 14th straight over Atlanta, holding on for a 3-2 victory that extended a streak dating to November 2005.
Philadelphia swept the season series again, outscoring the Thrashers 19-8 in four games. But the final meeting of the regular season went down to the wire as the home team rallied from a 3-0 deficit in the final period.
"We didn't make it easy on ourselves," Philadelphia's Scott Hartnell said. "But we got the points, and that's what counts. A win's a win. These two points are huge."
Carter's line, which includes Hartnell and Joffrey Lupul, had a hand in all the Philadelphia scoring. Hartnell assisted on both of Carter's goals, while Lupul scored with an assist from Carter.
"We see each other," Carter said. "When you stick together for a while, you get to know what the other guys are doing."
Carter scored his first just past the midway point of the opening period, beating Thrashers goalie Johan Hedberg to the glove side. The Flyers center added another goal, his 34th of the season, on a power play less than three minutes into the third to give the Flyers a 3-0 lead.
"The first couple of games this year, I didn't think they played that well," Nittymaki said. "This was actually the best game they played against us."
The result was the same, however.
Lupul scored his 16th goal in the opening minute of the second period after the Flyers caught the Thrashers on a line change.
With Colby Armstrong off for hooking, Carter seemed to put the game out of reach when he took a cross-ice pass from Hartnell and ripped a tough-angle shot past Hedberg before the goalie could slide across the crease. The puck somehow got through two Atlanta players, and Carter took advantage at 2:51 of the third.
But Atlanta rallied with a most unexpected weapon.
The Thrashers came into the day mired in a 1-for-33 slump on the power play. They failed in their first four chances against the Flyers before finally breaking through for a pair of goals with the man advantage.
Kovalchuk, celebrating the birth of his second child, got loose right down the middle and fired a shot that dribbled through Nittymaki's pads with 16 minutes remaining while Matt Carle was serving two minutes for cross-checking. It was Kovalchuk's 22nd goal.
Kozlov scored with 6:56 to go, beating Nittymaki from the right faceoff circle with Lupul was in the penalty box for boarding.
The Thrashers pulled Hedberg with about 90 seconds remaining and had a couple of good chances at sending the game to overtime before time ran out. Atlanta lost for the sixth time in seven games of a miserable season.
"We gave ourselves a chance to win," coach John Anderson said. "Our effort was way better. We played smarter. But it still wasn't good enough."
After Boulton delivered a hard check on a Flyers player, Cote skated in and started a fight with the Thrashers' brawler. The two dropped the gloves in front of the Atlanta bench and duked it out for nearly two minutes, both landing several big shots but neither going down before the linesmen stepped in.
Both were assessed fighting majors, but Cote also got an instigation penalty and a 10-minute misconduct.
- The Flyers won back-to-back road games over the weekend, also beating the first-place Bruins on Saturday.
- The Thrashers scored two power-play goals for the first time since a Dec. 30 game at Toronto.
- There was an extended delay in the second period when a pane of glass behind Philadelphia's net had to be replaced.
- Kovalchuk's wife delivered a boy Saturday morning. Both were doing well, expanding a family that already included a daughter.