Brad Marchand and Rich Peverley each had a goal and an assist while Milan Lucic and Tyler Seguin also scored for the Bruins, who had lost three of four coming in. Patrice Bergeron had two assists in the contest.
"I think we had a lot better effort today than we have in the past couple of games," said Boston head coach Claude Julien. "We did some more things on offense and defense and had good goaltending. The guys competed hard for all 60 minutes."
"We had a lot of chances, but Thomas came up big," said Washington head coach Dale Hunter. "A goalie as good as Thomas can beat you by himself some nights."
Boston scored just after the midway mark of the first as Peverley sent a pass from the high slot to the front of the net where Lucic was all alone and he waited out Vokoun to the left before lifting the puck in.
It was a 2-0 game with 1:22 to play in the first on Marchand's backhand from the low left side.
The second period passed without a goal as Thomas made 10 stops and Vokoun turned aside nine, but the Bruins made it a 3-0 game just 6:38 into the third.
Bergeron brought the puck into the Washington end from the right side and at the point fired a pass over to the left point. Marchand held it there and dished it down to the front where Seguin redirected it past Vokoun.
Washington got on the board with 7:56 to play when Johansson scored on a sharp angle shot from the left side on a rush play.
However, that was as close as it got and Peverley scored into the empty net with under a minute to play to seal the win.
Boston plays in Buffalo on Wednesday...Washington hosts Florida on Tuesday...The Capitals had taken a 5-3 decision over the Bruins in Washington on January 24...Neither side scored on the power play as Boston had three chances and Washington one.