Pavel Buchnevich scored twice and had an assist, and Jordan Kyrou had two assists for the Blues (2-1-0), who were coming off a 5-4 overtime win against the San Jose Sharks on Thursday. Jordan Binnington made 24 saves.
St. Louis was unable to overcome a multiple-goal deficit after doing so in each of its first two games.
“We got to play 60 minutes. That’s the goal,” Buchnevich said. “It’s hard to come back from two, three goals every time. It’s never going to happen. We have to play 60 minutes. We have to play well at the start of the game.”
Buchnevich gave the Blues a 1-0 lead at 6:47 of the first period, scoring on a backhand from the bottom of the left circle on the rush.
Eichel tied it 1-1 at 8:02, scoring around an outstretched Binnington.
Barbashev put Vegas ahead 2-1 at 18:13 on a shot from the low slot.
“[Barbashev’s] easy to read,” Eichel said. “He wins a lot of battles. He’s good on the walls. He’s got some underrated hands and a scoring touch in tight. He does a lot of little things that, as a centerman, make my job a lot easier.”
Theodore extended it to 3-1 at 2:55 of the second period with a slap shot from above the left circle.
Buchnevich cut it to 3-2 at 7:29 with a power-play goal on a wrist shot from the right circle.
“We move the puck pretty well in San Jose and here today,” Buchnevich said.
Nicolas Roy pushed it to 4-2 at 12:53 of the third period, redirecting Theodore’s shot from the left point.
“They were just adjusting the position and getting our middle guy higher for a high tip,” Theodore said. “We had two guys in the paint there. Obviously, ‘Roysy’ did a great job getting his stick on it.”