Justin Faulk scored at 5:39 of the second period to put the Blues ahead 2-1 on a wrist shot from the right circle, and Sundqvist made it 3-1 at 6:37, crashing the net on the left side on a loose puck in the crease.
Stone made it 3-2 at 9:10 after Brett Howden intercepted Faulk's outlet pass from his own zone.
Dorofeyev tied it 3-3 at 8:21 of the third period after Faulk mishandled a puck along the right boards. The puck went to the net and Dorofeyev tucked it across the goal line. It initially wasn't ruled a goal but was after the situation room informed the officials that the puck completely crossed the goal line.
"Giving up one late there stung," Golden Knights forward Colton Sissons said of Schenn's goal. "We thought we were going to get points out of it, but not our finest work.
"In the third, we really had some sustained offense. We did get some looks and I think that's when we were playing a little bit crisper and playing a little bit faster and a little bit more together. We were just a little bit sloppy, a little disjointed early on, especially in the first. Got to tune that up tomorrow at practice and put our best foot forward here."
NOTES: Vegas forward Jack Eichel returned and had three shots on goal in 19:34 after missing seven games with an undisclosed injury. … Golden Knights defenseman Brayden McNabb did not play and is week to week with an upper-body injury. His consecutive games played streak ended at 298; he was replaced by Jaycob Megna, who made his season debut and played 10:43. … Montgomery coached his 400th game on Friday; he is 232-120-48 with the Blues, Dallas Stars and Boston Bruins. … Jordan Kyrou was awarded a penalty shot at 3:44 of the first period but was denied with a glove save by Hart.