Elliott and Halak combined for a shutout, the Sharks put themselves in an early hole when Marc-Edouard Vlasic tapped the puck into his own net, and the Blues tied the first-round series at a game apiece with a 3-0 victory Saturday night.
Elliott made the final 17 saves after Halak left with an undisclosed lower-body injury early in the second period.
"The adrenaline kind of takes over, you forget about your body and just go out there and play," Elliott said. "You prepare every game like you're going to play, it's not like I was nonchalant before the game.
"When you get a chance you have to be prepared."
Vladimir Sobotka was credited with a goal on the first shot of the game after Vlasic's gaffe. David Backes and Andy McDonald also scored, and T.J. Oshie had two assists in the Blues' first playoff victory since April 12, 2004 against the Sharks.
Coach Ken Hitchcock was just as proud that his team held its own in a game that turned feisty at the finish. Blues defenseman Roman Polak and Sharks defenseman Justin Braun tangled and the ice was littered with gloves and sticks.
"Teams like San Jose, Detroit, Chicago, they play right through you, and if you don't push back you get pushed out the back door," Hitchcock said. "I was proud of our team that we fought back. If we didn't, this was going to be a short series."
Sharks coach Todd McLellan accused Sobotka of delivering a "sucker punch" to Dominic Moore after the final horn.
"If you're talking about the instigator, the sucker punch, the blow to the head, the broken nose, what do you think I thought about it?" McLellan said. "It's everything we want to get out of the game."
McDonald said T.J. Galiardi cracked his helmet with an elbow to the head in the third period. Galiardi was whistled for charging.
"It's a 2-minute penalty, but I'm sure they'll look at it," McDonald said. "It's a blatant blow to the head."
McDonald, who missed 51 games with a concussion sustained in October, said he was fine.
Vlasic didn't have much to say about his crucial mistake, except to say the puck was spinning and "it just popped up."
"Well, I mean, the game's easy when you're sitting in the press box, but it is what it is," Vlasic said to a reporter. "Do it nine more times and it won't go in."
Halak's left leg was bent underneath his body early in second period after Blues defenseman Barret Jackman slid into him. Halak finished with 12 saves.
The Blues announced midway through the second period that Halak was expected to return, but he never made it back to the bench. Elliott was hindered at the end of the regular season by an undisclosed upper-body injury, but was the backup for Game 1.
Hitchcock said Halak would be on the team flight to San Jose.
Halak and Elliott combined for 15 shutouts in the regular season, tying a modern NHL record, and won the Jennings Trophy for the fewest goals allowed. Elliott was quite the luxury as a backup after setting a modern NHL record with a 1.56 goals-against average and nine of the shutouts.
Antti Niemi made 29 saves for the seventh-seeded Sharks, who were shut out in both regular-season meetings in St. Louis, with Halak and Elliott getting one apiece.
Games 3 and 4 are in San Jose on Monday and Thursday nights.
The Blues set a franchise record with 30 home victories, but had dropped three in a row after losing 3-2 in double overtime in Game 1. They had the lead on the game's first shot, thanks to Vlasic's mistake.
Sobotka's wrist shot from above the left circle handcuffed Niemi, trickling between the goalie's pads, and was sitting in the crease. Vlasic attempted to swat it out on his backhand but instead tapped it into the net for Sobotka's third career playoff goal at 1:31.
The Sharks controlled play most of the rest of the period, and Joe Pavelski hit the goalpost with just under 7 minutes to go, but they couldn't get the puck past Halak.
Backes, who didn't take a shot in Game 1, made it 2-0 with a one-timer from Oshie at 13:49 of the second period. McDonald scored in the final minute with the Blues on a two-man advantage.
Elliott's regular-season numbers topped Halak's. But Halak got the nod the first two games likely because of past playoff success combined with Elliott's 1-2 record and 4.14 career goals-against average in the postseason plus the injury.
Elliott didn't face a shot for nearly 7 minutes as the Blues gave him plenty of time to get comfortable in the net, and when Backes made it 2-0 with just over 6 minutes left the Sharks had been outshot 13-6 for the period.
Elliott was tested at the end of the period, stretching for a toe save on Logan Couture's wraparound for perhaps his best save.
Notes: Cardinals pitcher Chris Carpenter got a huge ovation in the third period, displaying his two World Series rings with the camera panning out to the Blues shirt he was wearing. Among other luminaries at Game 2 were Cardinals teammate David Freese, Blues Hall of Famer Brett Hull and actor Jon Hamm.... The game was delayed a few minutes early in the first period when the Blues' bench broke. A replacement was installed between periods. ... Non-fighters Pavelski and Kris Russell tangled in the second period. Russell had no majors during the regular season and Pavelski had just one.