Ottawa had taken the lead in the first period when Lucas Raymond responded in the middle period.
The Swede stormed forward in a counterattack and took advantage of a return on Jake Walman's shot.
The tie was tied for the third period and Ottawa really pulled away from that.
Led by Mathieu Joseph, who scored three goals in the match, they were reduced to 4-1 before Raymond could comfort with six minutes left.
This time he steered in a well-balanced pass from Filip Hronek.
Lucas Raymond has now scored 22 goals and 52 points this season, which is the best of all rookies.
His two points against Ottawa means that he takes the step past Toronto's Michael Bunting, 26, who has scored 51 points.
Olofsson hero
A Swede who acted as a match hero last night was Victor Olofsson.
The hard-hitting forward already had an assist in the game against Nashville before stepping forward and deciding in the second period.
He did it in his characteristic way by a direct shot to the right in the attack zone.
The goal was Olofsson's fifteenth of the season and was the last in the match that Buffalo won 4-3.
Filip Forsberg scored a goal for Nashville.
- They made it difficult for us today, says Forsberg to NHL.com.
CLIP: Pettersson two-goal shooter for Vancouver (March 31)
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Pettersson two-goal shooter when Vancouver fell at home Photo: Bildbyrån