Pettersson made it 3-1 at 3:16 with a wrist shot off the rush that bounced off the glove of Lehner and landed between his legs, where it was knocked just over the goal line by the skate of Vegas defenseman Zach Whitecloud.
Michael Amadio scored on a deflection to make it 3-2 at 4:26, but Vancouver went up 4-2 at 13:03 on a 2-on-1 that started with Pettersson stealing a puck in his own end and finished with a no-look pass to Brad Richardson for a tap-in.
"The closer I got to the goal, the bigger Lehner looked, so I was lucky to have found Richardson there," Pettersson said.
Vegas had the first 11 shots and outshot Vancouver 17-5 in the third period. Theodore made it 4-3 at 5:27 with a far-side wrist shot from the right face-off dot.
"It was a great lesson to be learned, quite frankly," Boudreau said. "When you're playing a good team you can't sit back, and usually that lesson costs you, and it didn't cost us tonight, so it was a very cheap lesson learned."
NOTES:Stone, the Golden Knights captain, was minus-1 with three shots on goal in 17:17. … Eichel had one assist to extend his point streak to five games (four goals, two assists) … Lehner made his fourth straight start after missing 12 games with injury. … Horvat had a goal and an assist, giving him eight points (five goals, three assists) during a five-game point streak. … Chiasson extended his point streak to four games (three goals, four assists). … Pettersson has 14 points (eight goals, six assists) in the past eight games.