Nate Schmidt and Brock Boeser also scored for Vancouver, and Bo Horvat had two assists. Braden Holtby had 26 saves, including a penalty shot.
The Canucks sit eight points behind the Montreal Canadiens, who hold the fourth and final playoff spot in the North Division, but Vancouver has played five fewer games. The Calgary Flames are sandwiched in between, with four more points than the Canucks and having played six more games.
''Every game is a must win. You want to give yourself the best chance possible,'' Pearson said. ''Obviously we have games in hand, which could be the key for us. We've got to keep pushing, take it one game at a time and keep on staying in the win column.''
Vancouver's victory came after the Senators blanked the Canucks 3-0 on Thursday. Coach Travis Green liked a lot of what the Canucks did on Saturday, but saw room for improvement, too.
''Our game was solid in a lot of areas. I thought our five-on-five game was a lot better,'' he said. ''I just thought we almost shot ourselves in the foot a little bit tonight. We have to play a little bit smarter at certain times. We can't take that many penalties. ''
Evgenii Dadonov had a goal and an assist, and Colin White also scored for the Senators, who snapped a three-game winning streak.
Matt Murray started and stopped 12 of 13 shots before leaving wit an injury early in the second period. Marcus Hogberg had 18 saves in relief.
Senators had planned on starting Anton Forsberg in goal, with Murray acting as backup. However, Forsberg suffered a lower-body injury in warmups and did not take the ice.
''Things happen in the NHL and you got to adjust,'' Senators coach D.J. Smith said. ''But I thought we played good enough probably to get a point. We just played a little too wide open when the game was tied and it cost us.''
The teams continue their four-game series Monday and Wednesday night at Ottawa.
Dadanov tied the score at 2-2 with 8:08 left in the third, getting his 13th goal of the year with an unassisted blast that sailed over Holtby's glove and in.
Pearson gave Vancouver the lead less than 2 minutes later. Horvat streaked into the Senators' end and slipped a pass to Pearson at the top of the slot. Pearson took a few strides, then ripped a shot over Hogberg's stick for his ninth goal of the season.
Miller sealed the win with an empty-netter from the top of the crease with 54 seconds left.
The Canucks opened the scoring early, forcing a turnover deep in Ottawa territory and getting the puck up to Schmidt. The defenseman unleashed a long blast from the point and scored his fourth 1:43 into the game.
Connor Brown's shot from near the blue line hit traffic in front of the crease, where White and Virtanen battled for the puck. It hit Virtanen's skate and sailed in past Holtby, but White was credited with his ninth goal of the year at 8:32
Ottawa made a change in net 4:27 into the second after Murray and Vancouver's Jake Virtanen got tangled up in the crease. The goalie got his stick caught in the legs of the Vancouver right wing and hauled him down, prompting a tripping call. Murray also appeared to suffer an injury on the play and shook his leg before heading to the locker room.
Vancouver was quick to capitalize on Murray's tripping penalty. Quinn Hughes sliced a crisp pass to Boeser and he rifled it in from the right faceoff dot, beating Hogberg stick side for his 17th to give the Canucks a 2-1 lead at 4:46.
''We knew coming into this game that (the power play) needed to be difference makers because that was a key part of last game. To get one right away was huge,'' Boeser said.
Holtby was tested midway through the second after defenseman Tyler Myers was called for slashing Alex Formenton on a breakaway. The Senators' left wing was awarded a penalty shot but Holtby calmly tracked Formenton as he weaved in and turned the wrist shot away with his right pad.
The 31-year-old Holtby is looking freer and more confident than he did earlier this season, Green said.
''It's great to see,'' the coach said. ''He's a great person, a great teammate. He's had a great career so far, he's still relatively young. And it's awesome to see. I'm happy for him.''
Holtby called Saturday's victory a ''gutsy effort.''
''I thought it was one of those games that can go against you pretty quick if there's some saves at the other end, momentum goes that way,'' he said. ''I think our guys did a great job of hanging in there and making plays when they needed to.''
Vancouver was 1 for 4 with the man advantage. The Canucks got two minutes of 5-on-3 hockey in the third after Artem Zub and Erik Brannstrom were called for a high stick and cross-checking, respectively. Vancouver recorded just one shot on goal during the ensuing power play.
Ottawa failed to capitalize on five power plays, including a four-minute double minor Virtanen picked up midway through the second for a high stick that left Senators rookie Tim Stutzle with a bloody nose.
Vancouver's Jayce Hawryluk needed some minor medical attention in the first period after dropping the gloves with Brannstrom. The Ottawa defenseman had taken issue with Hawryluk squashing him along the end boards and the Canucks forward was quick to step up to the challenge. Each was handed a 5-minute major for fighting and Hawryluk winced while he held a bag of ice to his hand in the penalty box.
BACK IN THE LINEUP
D Alex Edler returned to the Canucks' lineup after serving a two-game suspension for a knee-on-knee hit on Toronto's Zach Hyman. Vancouver's Zack MacEwen and Tyler Motte played their first games since March 24.
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