"Yeah, for sure we are happy we got two points," said Niemi, who made 31 saves. "We played a good game, a good 60 minutes and we were able to get chances in all the periods. We played well, we just couldn't score."
Pavelski had a game-high 10 shots on goal, but it took a wrist shot in the second round of the shootout for him to put a puck past Varlamov.
"If we lose these games, it’s tough," Pavelski said. "You have to gather yourself and have the belief that it’s going to go in. I think that’s what the guys in here did. We believed it was going to go in and we would get a bounce and we did get one there."
The Avalanche had a power play for the final 1:05 of overtime after Marleau knocked Erik Johnson's stick from his hands with a slash, but they couldn't take advantage.
"If we expect to play perfect we're dreaming," Sharks coach Todd McLellan said. "It doesn't happen that way. There were lapses, but we're starting to put it together a little bit longer night in and night out. I thought we were aggressive, we were on our toes. We are still a work in progress."
The Avalanche have gone to overtime or a shootout in three of the past four games and lost them all. They've already permitted 40 or more shots on goal three times, lost one in regulation, one in overtime and one in a shootout.
"We're leaving Varly out to dry," said Avalanche left wing Jamie McGinn, who played against his brother, Sharks left wing Tye McGinn, for the first time at any level. "It's unacceptable. He stood on his head just like last year, except we pulled out a couple wins and this year we're not doing that. He's battling every night, it's amazing what he's doing back there for us."
Colorado took a 2-1 lead at 3:04 of the third period on a goal by Gabriel Landeskog, who skated into the left circle and beat Niemi low to the far side for his fourth goal, tying Tanguay for the team lead.
San Jose dominated the Avalanche in the first two periods, outshooting them 41-17, but the game was tied 1-1 because Varlamov made numerous big saves and Tanguay scored a second-period shorthanded goal at 13:24.
"He was outstanding, he made some incredible saves, especially in the first where we were struggling a lot," Avalanche coach Patrick Roy said of Varlamov. "After they took a 1-0 lead we just lost our focus. That part of the game was not very pretty for us."
The Sharks were on their second power play of the game after Avalanche defenseman Tyson Barrie was penalized for hooking when Varlamov dived to his right to prevent Pavelski from scoring at the edge of the crease.
Shortly after, Johnson lofted a clearing attempt that San Jose's Brent Burns tried to knock forward with his glove while standing at his own blue line. The puck landed behind him and Tanguay gained possession. He skated into the slot, stepped around Couture between the circles and found the back of the net.
Tanguay has four goals and two assists in a six-game scoring streak.
Varlamov made a save against Tommy Wingels on another power play later in the period and he made a pad stop on Marleau, who was open for a shot in the right circle with 5.6 seconds left in the period.
The Sharks have owned the first period this season, outscoring opponents 13-1. They dominated the Avalanche in the first, outshot them 23-8 and took a 1-0 lead that would have been much larger except for the play of Varlamov.
"It's unfortunate," McGinn said. "We said all the right things before the game, we were ready to, but then the Sharks just pounced on us and they were better than us in the first period. Varly gave us a chance to stay in it and win the game. Our second period was better but still not good enough. It's just unacceptable to have that kind of start. It's a big game and we have to start winning games."
Burns opened the scoring 9:23 into the first period. Burns drove to the net for a shot that Varlamov stopped, but Thornton corralled the rebound, came from behind the net and fed Mirco Mueller for a shot Burns redirected.
The Sharks outshot the Avalanche 19-2 after Mueller scored, launching 14 consecutive shots before Landeskog forced Niemi to make a stop at 15:21. Niemi made a nice glove save against Duchene, who was in the slot with 1.5 seconds left.
"I think we started pretty slow in the first period, but in the second and third we played well," Varlamov said. "We had lots of chances in the overtime, but we didn't score. Niemi played well. I felt pretty good, but we need points right now. Every point is very important. We want to win every game and there is frustration."