Alex Ovechkin (800 career goals) did not score in his second attempt to tie Gordie Howe (801) for second on the NHL all-time goals list. Wayne Gretzky leads with 894.
Sonny Milano had three assists for Washington (16-13-4), which has won six of its past seven games. Charlie Lindgren made 34 saves.
"A (few) of the things we talk about are defense and puck decisions and attacking the net," Capitals coach Peter Laviolette said. "Every guy has to do their job and they have to play hard, and we've gotten that on most nights. Guys have played hard. They've done the right things."
Auston Matthews had a goal and an assist for Toronto (19-7-6), which has lost its past two games after a 15-game point streak (12-0-3). Ilya Samsonov, who played the previous three seasons with Washington, allowed five goals on 28 shots in his first game back here. Samsonov was coming off consecutive shutouts and saw his streak end at 163:46.
"I think I played bad in this game," Samsonov said." A couple bad bounces, yeah. We need to get working. … For my game, I need to play better."
Gustafsson gave the Capitals a 1-0 lead at 11:12 of the first period, knocking in the rebound of Milano's shot at the right post.
William Nylander tied it 1-1 at 13:12 when he scored on a one-timer from the high slot off a pass from Matthews.
Trevor van Riemsdyk gave Washington a 2-1 lead at 14:48 when his shot from the left face-off circle deflected off Mark Giordano's stick and eluded Samsonov.
Van Riemsdyk has three goals in the past four games; he entered this season with 17 in 456.
"I was just trying to get it to the far pad. I didn't really have much," he said. "It was obviously really lucky to kind of hit his stick and bounce up into the air and get by 'Sammy' there. So, fortunate bounce, but we'll take it."