Capitals get OT win as Semin scores hat trick
Atlanta tied it on a goal by Evander Kane with 32.9 seconds left in regulation shortly after pulling goalie Chris Mason for an extra skater.
In overtime, however, Fleischmann banged in a backhander to provide the Capitals with their eighth consecutive home win over the Thrashers.
It was the fourth career hat trick for Semin, who came in with two goals in Washington's first seven games. Semin got his first goal in the second period and brought the Capitals back from a 2-1 deficit by scoring twice in the final 15 minutes.
Kane scored two goals, Andrew Ladd had one, and Mason finished with 40 saves. But it wasn't enough to prevent the Thrashers from absorbing their third straight defeat.
Mathieu Perreault had assists on Washington's final two goals in regulation. On the last one, Perreault skated from the right boards between the circles before passing to a wide-open Semin, who scored with 6:32 remaining.
Perreault was making his season debut after being called up from Hershey of the AHL before the game.
Michal Neuvirth had 29 saves to help the Capitals snap a two-game skid.
Washington trailed 1-0 before Semin cashed in on a mistake by Mason in the opening minute of the second period. Mason went behind the net and swept the puck around the boards, but Semin intercepted the clear in the right circle and scored on a drive that glanced off the left pipe.
The Thrashers regained the lead at 4:33 of the period when Rich Peverley wiggled free behind the net and sent a pass to Kane, who scored from the slot.
The Capitals got an apparent power-play goal at 11:42, but the officials waved off the goal after ruling the puck ricocheted off the skate of Washington defenseman Mike Green.
Semin tied it with 14:51 left, pouncing on the loose puck after Perreault was tripped while skating to the net.
Atlanta outshot the Capitals 13-4 in the first period and took a 1-0 lead when Ladd put in the rebound of his own shot with 58 seconds left and the Thrashers on a power play.
After scoring an NHL-leading 92 goals in first periods last season, the Capitals have been outscored 9-3 in the first frame thus far.