Lars Eller caught Holtby puck watching and passed through the goalie's legs to McMichael for a tap-in to make it 4-0 at 12:03 of the second period.
"I think we didn't forecheck well tonight," Stars defenseman Miro Heiskanen said. "And we probably didn't play that hard when we did it on the road."
The Capitals increased their lead to 5-0 when Nicklas Backstrom beat Holtby to the far side at 16:50.
"They're a skilled, fast team with a good forecheck as well," Backstrom said. "We talked about just moving the puck quick, that's something we've been struggling with lately, so just moving the puck quick and getting out of our zone as fast as possible. We did that good tonight."
Dallas, which had the third-best power-play percentage at home (26.1 percent), was 0-for-3.
"Their first power play, they generated a lot of zone time and a lot of puck possession," Washington coach Peter Laviolette said. "That was a little bit scary as well. I thought the penalty kill got better as the game went on too. Talented players over there, but I thought defensively we were good."
NOTES: Prior to the game, former Stars defenseman Sergei Zubov had his No. 56 retired. He played his final 12 NHL seasons (1996-2009) with Dallas and helped them win the Stanley Cup in 1999. The Hockey Hall of Famer is the Stars/Minnesota North Stars leader among defensemen in games played (839), goals (111), assists (438) and points (549). ... Holtby played last season for the Vancouver Canucks, who did not play the Capitals. He was 282-122-46 in 468 games with Washington, and is second in wins and games played behind Olaf Kolzig (301, 711) in Capitals history. His 35 shutouts are tied with Kolzig for most. ... Van Riemsdyk played his 40th game this season and had not scored since Jan. 30, 2021 (55 games). ... Washington has scored first in 30 games this season, most in the NHL.