Tampa Bay, which won the first two games of the best-of-seven matchup on the road, can advance to the conference finals with a victory at home on Wednesday night in Game 4.
"This team is a good team. It's going to be hard to win four games," Tampa Bay's Martin St. Louis said of the struggling Capitals. "Obviously we're happy about the result tonight and we just have to reload tomorrow."
Vincent Lecavalier and Sean Bergenheim also scored for the Lightning, whose sixth straight postseason win leaves them one victory away from reaching the East finals for the first time since Tampa Bay won its only Stanley Cup title in 2004. The Lightning haven't lost since falling into a 3-1 hole against the Pittsburgh Penguins in the first round.
"I think all year we've been pretty resilient," St. Louis said, "and I always feel like we give ourselves a chance."
The momentum shifted suddenly on Stamkos' fourth goal of the playoffs. The sellout crowd of 20,613 had barely stopped celebrating when Malone -- camped to the right of Capitals goalie Michal Neuvirth -- directed Nate Thompson's pass into the left corner of the net for a 4-3 lead with 14:13 remaining.
"I think we were waiting for things to happen in the second period, and our focus wasn't right," Lightning coach Guy Boucher said. "We just got back and reloaded and came out the way we're supposed to play. We had a lot of enthusiasm -- not being scared to lose but being hungry to win."
The stunned Capitals never recovered.
"They're uncanny when they want to get a goal. It's like they just snap their fingers or hit a button. They just dial it up," Knuble said. "You can see it's like they're flipping a switch. ... It leaves you flabbergasted. You don't know what to say about it."
Capitals coach Bruce Boudreau felt Malone's go-ahead goal should not have counted. But referees Paul Devorski and Dan O'Rourke didn't blow their whistles to wave it off or call a penalty.
"If you look at it, Malone is driving the net and he pushes our player into our goaltender, and he can't kick out his right leg to make the save," Boudreau said. "It's a no goal, no penalty call. It's one of the best referees in the league and I fully respect him, but I don't think it should have counted. That's my humble opinion."
Dwayne Roloson had 29 saves for the Lightning and again outplayed Neuvirth, who had 26 stops.
Boudreau said before the game that his team was confident it could get back into the series, noting that both games in Washington were tight and that a "little tweak" here or there and the Southeast Division champions may well have arrived in Tampa in a much better position.
After slipping into an even deeper hole, the Caps still insist they're capable of coming back to win the series.
"It's not over. They win three. We can win three," Ovechkin said.
"We want to take it back to Washington, and then anything can happen," Knuble said. "I don't know. You forget about this one, you get ready again."
The Capitals outshot the Lightning 13-8 in the first period, but Roloson stopped a couple point-blank shots and Washington cost itself a power play and an early lead when it was penalized for having too many men on the ice.
A little over three minutes after an apparent goal by Knuble was waved off, Bergenheim scored his second of the series -- fifth of the playoffs -- for a 1-0 lead. The Capitals erased that and jumped in front on goals by Knuble and Carlson that made it 2-1 with 12 minutes remaining in the second period.
Lecavalier, whose goal in overtime won Game 2, countered for Tampa Bay, beating Neuvirth from in front off a feed from St. Louis to make it 2-2.
Ovechkin assisted on Washington's first goal, sending a nifty backhanded pass to Knuble from the left corner. The two-time NHL MVP took advantage of a five-on-three power play, scoring on a rebound that put the Capitals up 3-2 late in the second.
But Neuvirth, a 23-year-old rookie, couldn't hold the advantage.
"We lapse for a certain amount of time," Washington forward Jason Arnott said. "We get up, and I think we think it's over and guys just relax a little bit. And then they just come. In the playoffs, you've got to be focused and ready on every shift. If you're not, bad things happen. It's another learning experience for us."
Washington defenseman Mike Green played just 59 seconds in the third period. "He got a lower-body injury," Boudreau said. It's not known whether Green will be available for Game 4 on Wednesday night. ... Ovechkin's power-play goal was the first of the series for the Capitals, who are 1-for-16 in the series. ... During the singing of the national anthem, blocks of fans passed a large American flag around a portion of the lower bowl of the arena. ... Tampa Bay left winger Simon Gagne and defenseman Pavel Kubina, both out because of undisclosed upper-body injuries, won't play before Game 5 at the earliest or the opener of the conference finals. "They're day to day, except for today and tomorrow," Boucher said. ... Boudreau said defenseman Dennis Wideman (leg injury) didn't make the trip to Florida.
Information from ESPN.com's Scott Burnside and The Associated Press was used in this report.