Marchessault’s power-play goal made it 4-3 at 5:31 of the third period. He scored his second of the game on a one-timer from the slot off a pass from William Karlsson.
Cotter tied it 4-4 at 9:44 with a wrist shot from high in the left circle.
Vegas had two scoring opportunities in the final seconds. Karlsson was open at the right post but couldn’t get off a clean shot with six seconds left. Vasilevskiy made a save on Eichel’s slap shot from the top of the slot and trapped the puck with three seconds left to preserve the win.
"I just tried to get it out quick knowing we didn't have a lot of time on the clock," Eichel said. "By the goalie’s reaction and some of the fans’ reaction I figured the puck was behind him. But he [found] a way to freeze it. There were a few of those instances tonight.
"… It's tough to swallow knowing that you did a lot of good things in the third period to give yourself a chance to win."
NOTES: Eichel extended his point streak to 12 games (19 points; seven goals, 12 assists). ... Marchessault has eight points (five goals, three assists) in the past six games. ... Vegas had 23 blocked shots. ... The Golden Knights are tied atop the NHL standings with the Vancouver Canucks (22-9-3). … Lightning defenseman Mikhail Sergachev did not play after injuring his foot against the St. Louis Blues on Tuesday and is day to day. ... Point has eight points (four goals, four assists) during a six-game point streak. He has 501 points (234 goals, 267 assists) in 533 NHL games. ... Stamkos (assist) has nine points (five goals, four assists) during a four-game point streak.