With the win, Vancouver has a small chance of reaching the playoffs as they chase a wild card in the Western Conference, seven points behind eighth-placed Dallas.
Vegas is currently also outside the Stanley Cup, but only one point behind Dallas.
Vancouver took a grip on the game during a 17-second period in the first period when they went from 0-1 to 2-1 through goals by Bo Horvat and Brad Richardson.
Pettersson shot at the Swedish goalkeeper Robin Lehner and the puck bounced out to Horvat who put it in the net.
- We got started at the right time.
We are hard to beat when we are in the lead, says Boudreau according to the Vancouver Sun.
In the second period, Vancouver increased to 4-1 through an assist and a goal by the Swede.
The 23-year-old steered in 4-1 on Oliver Ekmans-Larsson's shot.
Pettersson also got the last word when he put 5-1 at the beginning of the third period.
It was the fourth time in his career that Pettersson scored four points in a match, writes Vancouver Sun.
He is now up to 24 goals this season.
- It may have been his best match.
He was always close to the puck and played very intelligently.
He knows where to go and where to play, he sees the ice so well that when he turns he has everything on his forehand, says Boudreau.
- Pettersson sees in the same way as guys like Alex Ovetjkin.
Vancouver has never beaten Vegas before the start of the Golden Knights 2017.