The Capitals led 3-1 heading into the third period, before Mike Brown, Kris Versteeg and Tyler Bozak scored in a span of 3:03 for Toronto.
Semin tied it at 4 on a power play. Then he and Alex Ovechkin scored for Washington in the shootout, while Capitals goalie Michal Neuvirth stopped both of Toronto's attempts.
Nikolai Kulemin gave the Leafs a 1-0 lead at 14:29 of the first period before Mike Green, Jason Chimera and Tomas Fleischmann scored for Washington in the second. Devils 5, Blackhawks 3
CHICAGO (AP) - Rookie forward Bradley Mills scored his first NHL goal with 3:51 left in the third period to snap a tie, and New Jersey beat Chicago despite an injury to Martin Brodeur.
The star goalie left in the second period with a bruised right elbow. X-rays were negative.
Brodeur finished with eight saves. He was replaced by Johan Hedberg, who stopped 21 of 24 shots.
With nine points, the Devils moved out of last place in the league. New Jersey finished 2-4-0 on its road trip.
Jason Arnott and Travis Zajac also scored for the Devils, who won for the second time in seven games. Jamie Langenbrunner and Andy Greene had empty-net goals.
Viktor Stalberg, Brian Campbell and Fernando Pisani scored for the defending Stanley Cup champions. Stars 5, Penguins 2
DALLAS (AP) - Loui Eriksson scored twice, including a penalty-shot goal, and Kari Lehtonen made 21 saves as Dallas earned a fight-filled victory over Sidney Crosby and the Pittsburgh Penguins.
A frustrated Crosby, who entered with only four penalty minutes this season and rarely fights, squared off against Matt Niskanen at 12:33 of the second period while Pittsburgh trailed 4-1.
That was one of four bouts in the first two periods.
Stephane Robidas and Brad Richards each had a goal and an assist for Dallas. Steve Ott added a goal, and James Neal had two assists.
Tyler Kennedy and Matt Cooke scored for the Penguins, who have lost four of five (1-3-1). Coyotes 4, Predators 3
GLENDALE, Ariz. (AP) - Ed Jovanovski had the first three-goal game of his 15-year career and Phoenix overcame some early defensive miscues to beat Nashville.
Known as a hard-nosed defenseman, Jovanovski gave the Coyotes an unexpected jolt of offense with his hat trick, scoring the go-ahead goal with just more than 14 minutes left.
Lee Stempniak added his 100th career goal and Ilya Bryzgalov made 28 saves to help Phoenix pull out its second home win before another barely-there crowd of 6,761.
Francis Bouillon, Sergei Kostitsyn and Patric Hornqvist scored for Nashville. Bruins 5, Sabres 2
BUFFALO, N.Y. (AP) - Tim Thomas made 33 saves in his seventh straight win, and Brad Marchand and Michael Ryder had a goal and assist each to lift the surging Boston Bruins over Buffalo.
Thomas (7-0), who entered with a 0.50 goals-against average after consecutive shutouts, had his shutout streak of 167 minutes, 12 seconds snapped by Drew Stafford's second-period goal that made it 4-1.
Andrej Sekera also scored for Buffalo, which played without ailing goalie Ryan Miller. The Sabres came in with the second-fewest points (8) in the NHL after winning the Northeast Division last season.
Thomas allowed more than one goal for the first time this season, but tied a career high for longest winning streak.
Patrice Bergeron, Blake Wheeler and Milan Lucic also scored for Boston (7-2), which set a franchise record by winning its fifth consecutive road game to open a season. Hurricanes 7, Islanders 2
RALEIGH, N.C. (AP) - Cam Ward made 31 saves and Jon Matsumoto scored his first two NHL goals in Carolina's rout of New York.
Rick DiPietro played the whole game and allowed all seven goals on 32 shots as the Islanders lost their fifth straight.Joe Corvo, Eric Staal, Brandon Sutter, Jiri Tlusty and Jeff Skinner also scored for the Hurricanes. Sergei Samsonov had three assists, helping Carolina set a season high for goals.
The Hurricanes lost their previous two home games this season by identical 3-0 scores to Washington and Pittsburgh.
Michael Grabner and P.A. Parenteau had goals for the Islanders, who have been outscored 13-3 in their past two games. Thrashers 4, Panthers 3
SUNRISE, Fla. (AP) - Chris Mason made 52 saves and Fredrik Modin scored twice to lift Atlanta over Florida.
Dustin Byfuglien tied it for the Thrashers at 9:59 of the third period and Niclas Bergfors scored the game-winner 71 seconds later on a slap shot from the left faceoff dot.
Mason stopped 22 shots in the second period. The 55 shots by Florida tied a franchise record set on Dec. 18, 2005, in a 3-2 win at Washington.
Bryan Allen, Jason Garrison and Steven Reinprecht scored for the Panthers. Tomas Vokoun stopped 19 shots. Red Wings 2, Flames 1
CALGARY, Alberta (AP) - Mike Modano and Justin Abdelkader scored second-period goals to lead Detroit past Calgary.
The Flames led 1-0 after the first on a power-play goal by Mark Giordano before the Red Wings rallied for their fifth victory six games.
The Flames have lost three straight and finished their five-game homestand - their longest of the season - with a 2-3 record.
After missing the past two games with back spasms, Detroit's Jimmy Howard returned to the lineup and made 16 saves to improve his record to 5-0-1.
Calgary's Miikka Kiprusoff made 31 saves. Ducks 3, Lightning 2, OT
ANAHEIM, Calif. (AP) - Kyle Palmieri scored the tying goal late in regulation of his first NHL game and Ryan Getzlaf netted the winner 2:53 into overtime to lift Anaheim over Tampa Bay.
Teemu Selanne, who had a goal and an assist, hustled after a loose puck near the left boards just outside the blue line, stickhandled past defenseman Mike Lundin and circled the net before backhanding a pass to Getzlaf. The Ducks' captain won the game with his fifth goal this season.
Jonas Hiller made 32 saves for the win.
Blair Jones and Steven Stamkos scored for the Lightning.