Ivan Barbashev had a breakaway 1:45 into the third period but shot wide.
“We needed to do something to get us going, and we got the breakaway,” Cassidy said. “If we get that quick strike to tie it, it deflates the other team a little bit.”
Raymond then made it 2-0 at 4:51, cutting between two defenders, kicking the puck onto his stick and beating Samsonov for his 23rd goal and first since Feb. 22.
Vegas nearly scored midway through the third when Mark Stone’s shot trickled past Mrazek, but Dylan Larkin cleared the puck away from the crease.
Marco Kasper scored at 11:14, redirecting Erik Gustafsson’s feed into an open net for the 3-0 final.
The Golden Knights were held to five shots on goal in the third.
“They are a really good team, and we know that,” Kasper said. “We just tried to play a tight-checking game and tried to get some volume shooting.”
NOTES: Mrazek’s span of 2,611 days between shutouts for Detroit is the fifth-longest in NHL history by a goalie for the same franchise behind Pete Peeters (3,312 days with the Philadelphia Flyers), Bill Ranford (3,280 with the Boston Bruins), Brian Boucher (3,064 with Philadelphia) and Roberto Luongo (2,950 with the Florida Panthers). … Red Wings forward Patrick Kane had an assist in his 1,287th NHL game, which moved him past Phil Kessel for 10th all-time among United States-born players. … Jack Eichel’s eight-game point streak and Pavel Dorofeyev’s run of three games with a goal each came to an end.