Thornton set up Brent Burns' first-period goal and Logan Couture added a power-play goal early in the second to give the Sharks just enough offence to beat the Kings 2-1 Tuesday night to knot their series at two games.
"He's our leader for a reason," Burns said of Thornton. "Everybody keeps saying it. He's one of the hardest workers we have in here. It's awesome to play with him when he's playing like that. It's a lot of fun."
The Sharks outshot the Kings 15-3 in the opening period before falling into a shell the second half of the game, managing just four shots in the final 36:05 after taking a 2-0 lead.
Antti Niemi made 13 of his 22 saves in the third period to help the Sharks match Los Angeles' two home wins to open the series with two of their own.
"In the third it's typical, unfortunately the way it goes, usually teams are a little bit on their heels and the other team is pressuring, and you're just trying to find a way," defenceman Dan Boyle said.
"Obviously that's not the way we want to play, but that's the way it happens. A win's a win. That's what I've been talking about. We're in a good place right now, and it's only going to get harder."
Mike Richards scored a power-play goal and Jonathan Quick made 21 saves for the Kings, who have lost 10 of 11 road games dating to the end of the regular season.
Game 5 is Thursday night in Los Angeles when the Sharks will look to end a streak of four straight wins by the home team in this series.
"We knew going into this series we'd have to win one game at Staples Center if we want to win this series," Couture said. "We've done our job at home. We need to go into L.A. and win a game on Thursday. We're looking forward to it."
After falling behind 2-0, the Kings showed some fight in a dominant third period. They got on the scoreboard on a power play when Burns was sent off for boarding Anze Kopitar.
Los Angeles wore down San Jose's penalty killers in the offensive zone and scored when Richards knocked in a rebound of Jeff Carter's shot.
"I think we battled back and made it close but you don't get much for making it close," Kings coach Darryl Sutter said.
The Kings outshot the Sharks 14-2 in the third period, holding San Jose without a shot for nearly 13 minutes but couldn't get the equalizer against Niemi.
Couture gave the Sharks a 2-0 lead early in the second period, deflecting a point shot by Boyle past Quick while Colin Fraser was in the penalty box for roughing Andrew Desjardins in the offensive zone.
The Kings started to generate the better scoring chances after that, getting denied a goal midway through the period on an early whistle by an official. Los Angeles was unable to generate a shot on goal during two power plays later in the period with Jake Muzzin, shooting high with an empty net to cost the Kings a golden opportunity at a goal.
"For us, it's about how they dominated the first half of the game and then we dominated the second half of the game," defenceman Rob Scuderi said. "But they buried their chances. They play well here and we didn't learn from Game 3, so that's on us for not learning from our own mistakes."
The Sharks opened the game with one of their most dominating periods of the year to the delight of the boisterous crowd chanting "Beat L.A.! Beat L.A.!" from the start.
But San Jose had only one goal to show for that start thanks to solid play from Quick and a shot by Tommy Wingels that rang off the crossbar.
Led by the physically imposing line of Thornton, Burns and TJ Galiardi, the Sharks spent almost the entire first period in the Los Angeles zone.
San Jose jumped on top early when Thornton stole the puck from Slava Voynov on the forecheck and fed Burns, who shot was blocked. Thornton came up with the loose puck and slid a perfect cross-ice pass to Burns, who was not denied on his second chance, beating Quick with a one-timer.
"Burns has been shooting the puck real well so it was just a matter of time until he put one in the net," Thornton said. "After the first shot, the puck just came right back to me. He was open again and I just made the pass."
The Kings had to feel fortunate that was all San Jose managed for the period as they killed off two penalties and withstood constant pressure from the Sharks.
NOTES: F Kyle Clifford returned for Los Angeles after missing four games with an upper-body injury in place of rookie Tanner Pearson. ... Kings D Matt Greene, who played only five regular season games because of back problems, was in the lineup for the first time this post-season in place of Keaton Ellerby. ... F Tim Kennedy returned to the Sharks lineup in place of Marty Havlat, who left Game 3 after the first period with a lower-body injury.Suggest a correction