Ilya Kovalchuk also scored for the Thrashers (24-11-6), who got three assists from former Senator Marian Hossa.
Daniel Alfredsson and Tom Preissing scored for the Senators (21-18-2), who saw a four-game winning streak end.
Ottawa trailed 2-1 in the game until Preissing scored with less than four minutes remaining to force overtime. The defenceman’s point shot snuck by Kari Lehtonen for his third goal of the season.
There was no scoring in the first period although the Senators would have had a goal if not for the work of Thrashers defenceman Shane Hnidy.
Dany Heatley took a shot from along the boards that Lehtonen got a piece of, but still got through and trickled towards the goal-line, where Hnidy knocked the puck away.
Alfredsson opened the scoring in the first minute of the second period while the Senators were on the power play. The Sens captain got a quick shot away off a Heatley pass and beat Lehtonen.
Atlanta tied it just four minutes later when Kovalchuk beat Ray Emery with a hard point shot. That goal ended Emery’s home shutout streak at 155 minutes 42 seconds.
The Thrashers then took a 2-1 lead 6½ minutes later when Kozlov scored after Emery gave up a big rebound off a Hossa shot.
Notes: The Senators called up right-winger Jeff Heerema and centre Serge Payer from the AHL’s Binghamton Senators on an emergency basis for the game with Atlanta, although Heerema did not dress . . . The Thrashers called up forward Darren Haydar from the Chicago Wolves of the AHL, but he wasn’t in the lineup.