WASHINGTON — Alexander Semin scored one of Washington’s three power-play goals Thursday night and assisted on both of the others, including Mike Green’s go-ahead goal, and the Capitals held on for a 4-3 victory over the Atlanta Thrashers.

Green’s 23rd goal — most among NHL defensemen — came off passes from Nicklas Backstrom and Semin and snapped a 2-all tie 12:25 into the second period.

It came on a man-advantage, as did Washington’s first two goals, which came 53 seconds apart in the first period. But Ilya Kovalchuk scored later in the first on a power play for Atlanta — with the league’s leading goal-scorer, Alex Ovechkin, sitting in the penalty box — before Rich Peverly tied it.

After Green put Washington ahead, Eric Fehr added an insurance goal to make it 4-2.

Fehr’s 10th goal turned out to be quite important because Todd White scored a short-hander off Kovalchuk’s assist with just under 2 minutes remaining.

Washington also blew a 2-0 lead in its previous game, losing that one 4-2 to the Philadelphia Flyers. This time, Washington came back after allowing its edge to vanish, and goalie Michal Neuvirth won his second NHL start to improve to 2-0.

Semin got Washington going with his 23rd goal less than 41/2 minutes in. With White off for hooking, Semin took a pass from Sergei Fedorov just outside the blue line and split two Thrashers before putting a wrister into the upper-right corner. Ovechkin also was credited with an assist.

On the play, Eric Perrin was called for slashing Semin. So Washington went right back to work on the power play and capitalized again.

This time, off a pass from Semin, Green’s slap shot was blocked by Kari Lehtonen but trickled past the goalie as Brooks Laich tapped it in for his 15th goal.

It all amounted to further evidence that Washington’s power play is about as good as it gets these days. The Capitals entered with a 23.8 percent success rate, No. 1 in the Eastern Conference and No. 3 in the NHL, and just below the franchise record for a full season: 23.9 percent in 1984-85.

Atlanta cut the deficit to 2-1 while Ovechkin was off the ice. The league’s reigning MVP was called for roughing when he mixed it up along with boards with Marty Reasoner and Garnet Exelby. Ovechkin seemed to be looking for a fight after Peverly’s stick either hit — or came close to hitting — the Russian in the face.

Capitals coach Bruce Boudreau had a lengthy discussion with an official as Ovechkin skated over to serve his penalty, and the fans loudly expressed their displeasure with the call — chants that resumed after Kovalchuk’s 32nd goal came off assists from White and Slava Kozlov.

The Thrashers made it 2-all about 4 minutes into the second period on Peverley’s eighth goal. He got behind Washington’s defense on a breakaway with a pass from Niclas Havelid.