Thornton had missed five straight games with an infected elbow before returning Friday, when Boston was defeated, 3-1, at Atlanta. In that game, Thornton was ejected in the first period for joining a fight. On Saturday, Thornton got his 22nd goal of the season and 300th NHL point as Boston improved to just 4-14-1 in its last 19 games.
The Bruins have not won back-to-back contests since a three-game winning streak from December 5-8.
The Capitals are coming off consecutive regulation losses after tying a franchise record by picking up a point in 14 straight games (8-0-3-3).
On Saturday, Michael Nylander and Robert Lang scored for the Capitals in a 5-2 road loss to the Ottawa Senators. All-Star right wing Jaromir Jagr left in the second period with a groin injury and is listed as day-to-day.
Washington is trying to avoid losing four in a row for the first time this season.
The Capitals and Bruins have split a pair of meetings this season. Boston posted a 7-2 win here on October 30 and is 4-1-0 in the last five home matchups.