Todd Marchant had a goal and two assists, and Jean-Sebastien Giguere made 26 saves to help stop Washington's four-game winning streak. Giguere's bid for a second consecutive shutout ended with Alexander Semin's goal 5:06 into the third period, off an up-against-the-boards, through-the-legs pass from Alex Ovechkin.
Thornton was called up from the minors during the day and immediately produced his first NHL goal since the 2003-'04 season, when he played for Chicago. It was an eventful evening for the right wing: He served a five-minute penalty for fighting in the first period, and assisted on Dustin Penner's goal in the second period that made it 3-0.
Selanne, Andy McDonald and Corey Perry all scored in the final period for Anaheim (22-3-6, 51 points), which is off to the best start in franchise history. Selanne has eight points in the past four games.
Ovechkin's only NHL hat-trick came against Anaheim last season, but Giguere and his defence did a good job of holding the reigning rookie of the year in check, limiting him to one shot in the first period and six for the night. He did come up with that one brilliant pass, though, while being pinned against the boards in a corner.
Washington averaged 5 1/2 goals during its previous four games, but the Ducks dominated the flow of play for long stretches, outshooting the Capitals 8-0 over the first six minutes of the second period and 34-27 for the game.
During the opening minute, Marchant slid the puck over to Thornton, who moved in alone in front of the net and sent a backhander into the upper right corner.
That marked the first time Washington had trailed in any game since a Nov. 25 loss to the Islanders. Since then, the Capitals had reeled off their winning streak, during which they outscored opponents 22-11 - including 9-1 in the first period.
But the Ducks would double their lead later in that period on a short-handed goal, helped by Capitals goalie Olie Kolzig's gaffe. Kolzig partially whiffed when attempting to clear the puck from behind his net, allowing Marchant to gather the puck and deposit it for his eighth goal of the season.
To that point, less than 15 minutes into the game, Anaheim had taken four shots - two had gone in. Penner then beat two defencemen to a loose puck 7:16 into the second period to pad the visitors' lead.
Notes: Anaheim matched its season best for scoring; this was its sixth game with six goals. ... The Capitals were trying to win a fifth consecutive game for the first time since March 3-11, 2001. ... Washington also failed to become the only team to beat Western Conference-leading Anaheim and East-leading Buffalo this season. The Capitals defeated the Sabres 7-4 last Saturday. ... Anaheim improved to 16-0-2 when leading after two periods. ... Anaheim opened a five-game road trip and a stretch in which it plays 10 of 12 away from home.