It was the first National Hockey League championship for the franchise in their first Stanley Cup finals appearance since 1998.
With the Stanley Cup in the building at T-Mobile Arena on Thursday, a two-time Cup victor took in the game as well.
The Golden Knights are 16-2 in their last 18 games versus a team with a winning road record.
A scoreless first period gave way to a wild second period with five goals, two ties and a lead change that temporarily put the Golden Knights ahead. Things are much reversed on the spread, where the Knights are +205 laying 1.5 goals while the Caps are +220 getting the goals. The Capitals will face that prospect in Game 5 against a Vegas Golden Knights team that has played strong at home. Yet for all of his goal-scoring prowess and athletic swagger, the Great Eight had never won an Olympic gold medal or a Stanley Cup title. Tomas Tatar redirected it toward the net as Djoos and Perron fell into Holtby's way.More news: Maria Sharapova fires back at Serena in book feud
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The play was reviewed for goalie interference, but eventually stood and tied the game 2-2 late in the second period. Eller then fired the rebound into the vacated net.
Moments later, the Knights struggled to keep up with the Caps' puck movement and Brett Connolly open for a shot.
Eller outmuscled Vegas defender Luca Sbisa for the puck, which was sacked at the net by Brett Connolly and squirted through the pads of Vegas goalie Marc-Andre Fleury before it stopped on the edge of the crease.
The offensive chances were held to a minimum on both sides in the first period of Game 5, with the best opportunities coming for Washington on the lone power play of the opening frame. Washington is the 19th active franchise to win the Stanley Cup. Three of those players had multi-point games.