In a single nine-minute stretch of the third period, the Washington Capitals dramatically took the lead before the Vegas Golden Knights replied with two goals of their own. Washington's Tom Wilson also flattened Vegas forward Jonathan Marchessault with a blindside hit that could reverberate through the Stanley Cup Final.

After 10 goals and a Final-record four lead changes overall in a fantastically entertaining opener, it's tough to imagine what these unlikely opponents will do for an encore.

But the upstart Golden Knights have spent their entire inaugural season speeding past all expectations, and their first Final game didn't slow them down in the slightest.

Tomas Nosek scored the tiebreaking goal midway through the third period, and the expansion Golden Knights surged past the Capitals for a 6-4 victory on Monday night.

"We put fun ahead of everything, and you can tell," said Ryan Reaves, who scored the Knights' tying goal in the third period. "Guys have are having fun and they're smiling."

The Eastern Conference champion Capitals hadn't given up this many goals in 29 games since March 18, but they hadn't seen anything like this charmed run by the upstart Knights. With its sellout crowd of hometown fans at deafening volume all night, Vegas put its usual speed and relentlessness on full display while overcoming that third-period deficit to win the opener of a matchup between two franchises seeking their first Stanley Cup titles.

Marc-Andre Fleury made 24 saves in an occasionally shaky performance, but the three-time Stanley Cup winner's new teammates carried the goalie who has so often carried them with a relentless outburst of offense.

"We're a good defensive group, but we weren't tonight," Marchessault said. "They're a team that's very fast in the neutral zone, and we gave them too much respect with the puck. We need to be faster in the defensive zone. We're going to fix that in our game."

The Game 1 winner has won the last six Cups and 61 of 78 overall.

Braden Holtby stopped 28 shots for the Capitals, whose first Stanley Cup Final game in 20 years was a defensive nightmare. Washington still played a strong offensive game and had chances to win, but never slowed the Knights.

"I think next game is going to be different, and all the nervousness, all the bad thing goes away in this game," said captain Alex Ovechkin, who had an assist. "We just have to forget about it and bounce back (in the) next one."

Wilson got credit for the goal that put the Caps up 4-3 early in the third period when Fleury back-heeled a loose puck into his own net, but Reaves evened it 91 seconds later for Vegas.

Nosek then put the Knights ahead after Shea Theodore kept the puck in Washington's zone, sidestepped a defender and fired a beautiful cross-ice pass to the Czech forward, who buried a one-timer for his second goal of the playoffs.

Colin Miller, William Karlsson and Reilly Smith scored early goals before Nosek added an empty-netter for the Knights, who are three wins away from one of the most improbable championships in recent North American team sports history. Just 342 days after the Knights selected the backbone of their first roster in the expansion draft, Vegas had another party on the Strip with its remarkable collection of castoffs.

Brett Connolly, Nicklas Backstrom and John Carlson also scored for Washington, but its biggest stars didn't match the Knights' outburst. Along with Ovechkin's quiet night, Evgeny Kuznetsov — who scored a whopping 24 points in the first three rounds — also had just one assist.

The Golden Knights' playoff pregame shows have been a celebration of Vegas showmanship, and their first Final game started with an extravaganza that included archers, a trebuchet and a spectacular light show.

And then the Knights and Caps put on a high-energy production of their own with plenty of fireworks and drama.

With none of the customary caution or high-pressure effects often shown by teams and players in their first game on the NHL's biggest stage, Vegas and Washington jumped right into an up-tempo thriller. Vegas had outscored its opponents 10-0 in the first period at home during the playoffs, but the Caps got two goals.

After Miller scored the Knights' first goal on a power play and ended Holtby's scoreless streak at nearly 167 minutes, Washington calmly surged ahead later in the first period with goals 42 seconds apart.

The wild scoring continued in the third with an own-goal by Fleury, who lost track of a rebound and kicked it backward into his net.

T-Mobile Arena was only quiet for a few seconds before the tying goal from Reaves, who cross-checked Carlson to the ice an instant before the puck unexpectedly bounced to him for an uncontested shot.

Reaves didn't score at all in his first 26 games after joining the Knights in a trade, but the rough-and-tumble forward broke through with the winning goal in the Western Conference finals clincher against Winnipeg.

Wilson delivered his crushing open-ice hit moments later to Marchessault, who was shaken up on the play. The Golden Knights uniformly criticized it as a late hit, while the rambunctious Wilson defended himself.

"I haven't obviously slowed it down and looked at it, but I think he'd probably say he shouldn't have admired his pass, and I'm just finishing my check," Wilson said.

"I think the league is going to take care of it," Marchessault said. "I never see him coming. Puck is away for a couple seconds for sure. But whatever. He's a guy who plays hard, throws big hits out there."

NOTES: Vegas is aiming to be the first franchise in a major North American professional league to win a title in its first season since the 1950 Cleveland Browns, who entered the NFL as a fully formed team after four seasons in the AAFC. ... Vegas D Deryk Engelland had two assists after going scoreless in the first 15 playoff games. ... Vegas improved to 11-1 in the postseason when scoring first.