Stephenson gave the Golden Knights a 1-0 lead on a one-timer 28 seconds into the first period. It was Vegas' only shot on goal in the first 6:58.
Stephenson scored to make it 2-0 at 14:44 when Theodore stole the puck in his zone and made a stretch pass for a breakaway.
William Carrier scored off another Ducks turnover to make it 3-0 at 6:12 of the second period. Alex Pietrangelo stole the puck from Shattenkirk at Anaheim's blue line and brought it to the top of the right circle before centering a pass to Carrier for a one-timer.
"There were parts of the game where we did very good things, but we just kept giving them the puck back," Eakins said. "Our turnover rate tonight was high, and if you turn over a puck against a team like that, they will make you pay."
Lehner's shutout streak ended at 154:02 when Steel scored on a rebound to make it 3-1 at 2:00 of the third period. William Karlsson scored off a rebound to make it 4-1 at 5:39.
"As a group, we're scoring up and down the lineup," Golden Knights defenseman Alex Pietrangelo said. "That'll alleviate some of the pressure for the top guys."
Theodore scored on a one-timer from inside the right point at 7:17 for the 5-1 final.
"I feel like we have a lot of guys scoring right now, which helps," Theodore said. "I'm just trying to move the puck around and hopefully guys stay this hot."
NOTES: Vegas forward Tomas Nosek left in the first period, and forward Nicolas Roy did not play in the third. DeBoer did not have an update on either player. Nosek did not play at Anaheim on April 16 because of undisclosed injury. ... The Ducks have gone 22 straight home games without a win in regulation (3-16-3). … Golden Knights forward Reilly Smith missed his third straight game with an undisclosed injury sustained against the Ducks on April 18. ... Anaheim defenseman Josh Manson missed the game after he was injured during a 4-1 loss to the Los Angeles Kings on Tuesday. ... Ducks forward Isac Lundestrom has returned to practice after having his appendix removed April 8, but he missed his eighth straight game.