Semyon Varlamov, who got the nod over Jose Theodore, made 26 saves in his first start of the series for Washington, which has won two in a row after losing the opener 3-2 in overtime.
Boyd Gordon, Brooks Laich and Eric Fehr each scored within a span of 7:27 as the Capitals chased Jaroslav Halak 8:33 into the second.
Ovechkin dropped to his knees at 13:50 to put a one-timer past Carey Price, who relieved Halak after Washington took a 3-0 lead.
Tomas Plekanec spoiled Varlamov's shutout bid with a power-play goal 2:25 into the third.
Matt Bradley scored the Capitals' final goal with 44.1 seconds left in the third.
Game 4 is Wednesday night in Montreal.
Varlamov got his second straight win since relieving Theodore early in Game 2.
Theodore, the 2002 Hart Trophy winner as league MVP with the Canadiens, was pulled after allowing goals on Montreal's first two shots Saturday. Varlamov stopped 19 shots the rest of the way for the win in Washington's dramatic 6-5 comeback victory in overtime.
Two nights later, Halak was yanked after he was beaten on three of six shots in the second. The Slovakian goalie stopped 10 shots overall. Price made 22 saves.
Washington's special teams play opened the scoring early in the second as Gordon scored a short-handed goal to put the Canadiens up 1-0.
The Capitals, who boast the NHL's top-ranked power play, have not scored a goal with the man advantage in five straight games, including the last two of the regular season.
Gordon, who did not dress for Game 2, backhanded his own rebound past Halak for his first goal 1:06 into the second. Canadiens defenseman Jaroslav Spacek slid backwards into Halak, pushing the Canadiens goalie into his own net and clearing the way for Gordon's shot.
Laich added his first goal at 4:42 to make it 2-0 before Fehr scored his second goal in two games, ending Halak's outing with Montreal in a 3-0 hole before the midway through the second.
The Bell Centre crowd cheered as Price skated onto the ice.
Booed whenever he touched the puck, Ovechkin increased the lead to 4-0 when he snapped Nicklas Backstrom's feed past Price for his second goal in two games.
Plekanec drew Montreal to within three early in the third.
Canadiens legend Jean Beliveau drew a huge cheer when he was shown on the video scoreboard through the final bars of "O Canada" prior to the game.
The sellout crowd of 21,273 roared its approval for the end-to-end action through the first half of the opening period, rising to its feet in a standing ovation during a stoppage in play 11:54 in.
Varlamov held the game scoreless through one as he turned aside several good Montreal scoring chances as the Canadiens held a 10-7 edge in shots after the first.
Notes
Canadiens C Glen Metropolit returned after missing the last six regular season games and first two of the playoffs because of a shoulder injury. … RW Sergei Kostitsyn was left out of the lineup, and C Ben Maxwell and D Ryan O'Byrne also were not in uniform for Montreal.