MONTREAL -- The Montreal Canadiens are off to their first Stanley Cup final since 1993.
Carey Price stopped 37 shots for Montreal, which will look to end Canada's championship drought that stretches back to the franchise's last title 28 years ago.
The Canadiens, who improved to 5-1 in OT in these playoffs, are set to meet either the Tampa Bay Lightning or New York Islanders in the final. That semifinal matchup sits tied 3-3 with Game 7 set for Friday in Tampa.
Reilly Smith and Alec Martinez replied for Vegas. Lehner, who won Game 4 by a 2-1 scoreline in overtime at the Bell Centre but watched Montreal's 4-1 victory in Game 5 in Sin City with Vezina Trophy finalist Marc-Andre Fleury back in the crease, finished with 29 saves.
William Karlsson added two assists.
The frustrated Golden Knights finished the regular season second in the NHL's overall standings -- 23 points ahead of the 18th-ranked Canadiens -- but much like the heavily favoured Toronto Maple Leafs and Winnipeg Jets before them, had no answer for a relentless opponent that's spent much of the last two months confounding the hockey world.
Thursday was Saint-Jean-Baptiste Day in Quebec, and there was more to celebrate than usual as the Canadiens will now look to bring the sport's Holy Grail back over the border after Vancouver (1994 and 2011), Calgary (2004), Edmonton (2006) and Ottawa (2007) all fell short in the final since Montreal's triumph 28 years ago.
Down 2-1 to start the third period, Vegas got even at 1:08 when Price was handcuffed by Alex Pietrangelo's initial shot that fell to Martinez for the defenceman to bang in his fourth.
The Golden Knights continued to push and had a couple chances to grab the lead before Lehner denied Danault from the slot as the teams headed to their third straight OT game at the Bell Centre after splitting the first two.
Caufield snapped a 1-1 tie at 9:36 of the second when he chipped a pass from Joel Edmundson past Brayden McNabb and raced around the Vegas blue-liner before firing upstairs shortside on Lehner for his fourth goal of the series.
The 20-year-old had some choice words -- "It's good that he opened his mouth about it" -- after the Vegas goaltender stopped Caufield on a breakaway in Game 4 and then told reporters the pre-scout suggested the Montreal winger was going to go-five hole.
The Bell Centre crowd rained down "Lehner! Lehner!" chants as thousands more well-lubricated fans celebrated on the streets outside the arena.
Caufield became the first player his age or younger to score four times in the third round since Jordan Staal with Pittsburgh in 2008.
Vegas got a power player shortly thereafter, but fell to 0 for its last 17 and 4 for 42 in the post-season.
Montreal, meanwhile, killed off its 30th straight man advantage dating back to Game 4 against Toronto.
The Canadiens didn't need Price to be the difference much in the series, but he made an outstanding pad stop on Karlsson from the slot off a Martinez feed later in the period before also denying Smith on a backhand chance.
With similarities to the team's memorable run in the spring of 1993 -- an underdog not expected to challenge the big boys -- Montreal is into its NHL-record 33rd final since 1917-18 and will be looking to add to its league-topping 24 Cup banners.
The Canadiens clinched a berth in the title series on home ice for the seventh time since the league expanded in 1966-67, and the first since defeating the Islanders in Game 5 at the Montreal Forum on May 24, 1993.
Montreal advanced to the Eastern Conference final in both 2010 and 2014, but lost out to the Philadelphia Flyers and New York Rangers, respectively.
Fans gathered outside the Bell Centre in the hours before puck drop on a sun-soaked Montreal holiday evening, with many wearing Canadiens jerseys, waving the province's fleur-de-lis flag -- or both.
With general manager Marc Bergevin looking on from a private suite in his lucky red suit, the Canadiens opened the scoring on the power play in the first period. Martinez's stick exploded on a clearing attempt and the puck fell to Weber, who ripped his first of the post-season past a screened Lehner at 14:06.
But the Golden Knights replied 48 seconds later when Smith redirected his first of the series, and third of the playoffs, at the lip of Price's crease off a nice feed from Shea Theodore.
Vegas was out of sync most of the series following a 4-1 victory in Game 1 -- a lot of that had to do with Montreal's suffocating style and pressure -- as a top-6 forward group of Smith, Karlsson, former Canadiens captain Max Pacioretty, Mark Stone, Chandler Stephenson and Jonathan Marchessault combined for two goals.