DENVER (Ticker) -- The best player during the regular season sent the best team during the regular season back to the Stanley Cup Finals.
The favorite for the Hart Trophy as the NHL's most valuable player, Sakic got to a rebound and flicked a backhander by goaltender Brent Johnson after the rookie stopped Alex Tanguay's deflection but could not find the puck.
"(Rob Blake) just let it fly and the rebound was there with an empty net," Sakic said.
Sakic's league-leading ninth playoff goal and fourth career postseason overtime tally set off a wild celebration and moved teammate Ray Bourque one step closer to an elusive Stanley Cup.
"I'm very happy," said Bourque, who has played more regular-season and playoff games without winning a championship than anyone in NHL history. "This is why I came here, to give myself another opportunity. It's been a long time coming."
The Avalanche went on the power play after Blues defenseman Alex Khavanov received a double-minor for high-sticking Milan Hejduk with 2:16 left in the third period.
"The guy didn't leave the ice after that. It's very questionable and it's up to the referee. Whatever they said was called, it's his decision," Khavanov said. "I just got my hands in front of me, I didn't try to get him in the face. I just saw him coming and I pushed the puck forward and I just tried to protect myself."
"It's tough," teammate Scott Mellanby added. "(The referee) had the courage to make the call, so I guess you have to give him credit for that, but usually there is some visible blood. You go down on the ice and roll around, I guess you get that call. It's hard when you work hard and have a call like that be the difference, but we are not going to use that as an excuse."
Colorado had trouble mounting an attack during regulation but ended the shortest extra period of this year's playoffs and recorded its second straight overtime triumph.
The Avalanche returned to the Stanley Cup Finals for the first time since winning the championship in 1996. They will host Game One against the winner of the Eastern Conference finals between the New Jersey Devils and the Pittsburgh Penguins.
"This is huge," Colorado defenseman Adam Foote said. "It's so hard getting there. We've been close a lot and now it's just the beginning. We've got a job to do and this is just the start of it. We can enjoy this for a couple hours and then move on and stay focused for the next series."
The defending champion Devils have a three games to one lead and can end that series at home on Tuesday night.
Sakic helped make up for the absence of Peter Forsberg, who underwent an emergency spleenectomy after Game Seven of the conference finals and will miss the rest of the playoffs. Despite playing with a sore shoulder, Sakic had four goals and four assists in the series.
"Joe is unbelievable. He came up big again tonight," said Avalanche center Stephane Yelle.
Appearing in the conference finals for the first time since 1986, St. Louis never got untracked. The Blues led for only 52 seconds in the series and just once scored more than two goals against Patrick Roy.
"Everybody in here realizes we left a little bit on the table, especially the first three games and getting off to as bad a starts as we did, giving up one, two, three goals," St. Louis captain Chris Pronger said. "It's tough to come back. That was kind of our death, I guess. Against a team like that that plays as sound defensively, it's tough coming back each and every night."
Johnson was the surprise starter for St. Louis, although Roman Turek surrendered three goals in the first period in Game Four. The 24-year-old responded with 34 saves, including 26 over the first two periods.
But Roy made the biggest stop. With 11 minutes left in the third and the game tied, 1-1, the winningest goalie in NHL history got his left pad on a deflection, then robbed Pavol Demitra with a glove save from point-blank range. Limited to two assists in the series, Demitra slammed his stick against the boards in frustration.
Johnson came up big in a scoreless first period, getting his left pad on Blake's blast from the top of the left faceoff circle, making a right arm stop on Chris Drury's wrist shot from the slot and stopping Drury again during a power play.
Colorado appeared to get on the board with six minutes to go in the period, but referee Dan Marouelli immediately waved off Ville Nieminen's power-play goal, ruling he pushed it in with his arm.
The Avalanche were back on the power play in the second period following a cross-checking penalty on defenseman Sean Hill at 9:23. With just three seconds left on the advantage, Blake slid a short pass to Hejduk, who got away from Khavanov's check and slipped the puck between Johnson's pads on Colorado's 19th shot.
It was the seventh playoff goal for Hejduk, who leads all scorers with 20 points.
The lead lasted barely two minutes. With 6:29 left in the period, Cory Stillman had the puck behind the net and backhanded a pass in front to Bryce Salvador. The rookie defenseman put a wrist shot from the bottom of the left circle into the top right corner of the net for his second playoff goal and first since scoring the overtime winner in Game Five of the conference quarterfinals.
Mellanby nearly put the Blues in front in the opening minute of the third period, but Roy got the tip of his right skate on his backhander, which skidded just wide of the left goalpost.
Roy made 28 saves and is headed to the Stanley Cup Finals for the fourth time. He won championships in his first three trips, two with the Montreal Canadiens (1986, 1993) and one with the Avalanche (1996).
St. Louis has not reached the Stanley Cup Finals since 1970.