Chris Stewart and Ryan Reaves scored for the Blues on the first five shots of the game, but Thomas stopped the next 27 shots to give the Blues their first regulation loss to an Eastern Conference team in 15 games this season.

St. Louis, 26-4-4 at home, last lost at home in regulation 5-2 decision to Chicago on Dec. 3, 2011.

Marchand and Milan Lucic scored in the first period to give the Bruins a 2-0 lead. Marchand pushed the lead to 4-2 midway through the third period with his 21st goal of the season.

SENATORS 5, CAPITALS 2

OTTAWA (AP) - Erik Karlsson and Milan Michalek each had three points.

John Carlson and Mathieu Perreault scored for the Capitals, who have lost three straight. Alex Ovechkin missed the game with a lower body injury and is listed as day-to-day.

Karlsson finished with a goal and two assists to set a new franchise record for assists by a defenceman in a season with 47.

The 21-year-old now has seven points in his last two games. His 60 points on the season give him a 20-point lead on Florida's Brian Campbell for the NHL lead in scoring by a defenceman.

Michalek added two goals and an assist, while Chris Phillips, with his fourth goal in six games, also scored for Ottawa. Craig Anderson made 33 saves.

Nick Foligno scored into an empty net for Ottawa.