Spooner, an Ottawa native, gave the Bruins a seven-point edge over the Senators for the second wild card into the Stanley Cup Playoffs from the Eastern Conference.
The Bruins moved six points ahead of the Florida Panthers, the closest team to them for the second wild card.
Spooner scored his second and third goals of the season for the Bruins (34-22-10), who are 6-1-1 in their past eight games.
Spooner said he was asked by some friends to take it easy on the home team.
"I had a text actually from about four of my friends," Spooner said. "They said, 'You guys cannot win tonight. You've got to let the Sens win, they need to catch you.'
"I was like, 'That's not going to happen.' It was good."
"After the second period I even mentioned it, you were up 3-0, you can thank your goaltender because we did a poor job of reloading," Bruins coach Claude Julien said. "They were coming at us on the rush, and for whatever reason there was a lot of standing still.
"They had us on our heels from the second period on, and if it wasn't for Tuukka, it could have been a different outcome. Having said that, we won a big game. They don't all have to be pretty at this point, but they have to be successful, and that's the most important thing."
Rask said, "It wasn't easy today. I thought the first period was our best period, and after that we didn't play our best, but we got the win and that's all we need."
The Senators (30-24-11) lost for the fourth time in their past 14 games (10-2-2). Rookie Matt Puempel scored his first NHL goal.
Ottawa goaltender Craig Anderson, playing his second straight game since returning from a bruised hand that kept him out of the lineup for 17 games, made 19 saves.
Cameron said he thought Anderson played a good game and said of possible second guessing, "This job will be available eventually, just apply for it."
Spooner opened the scoring on a power play 62 seconds into the second period, and the Bruins took control with goals by Eriksson and Spooner 92 seconds apart later in the period.
Eriksson scored his 17th of the season at 15:21. With the teams playing 4-on-4, Eriksson chased down a puck in the Ottawa zone. Senators defenseman Cody Ceci came off the bench and tried to play the puck instead of taking the man and was unsuccessful.
Eriksson jumped around Ceci and went wide around Anderson, tucking the puck into the open net.
Spooner scored his second at 16:53 when Bruins forward Milan Lucic put the puck toward the net and the puck went in off Spooner at the edge of the crease. The play was reviewed, but it was judged there was no distinct kicking motion by Spooner.
"[Spooner] was good tonight. Scoring that first goal was huge to give us that lead," Julien said. "Great shot on his part. I was just as impressed by his second goal where he drove to the net hard and stopped.
"[Lucic] did a heck of a job on that, outsmuscling the defenseman and getting that puck to him. It was nice to see him score a couple of goals in his hometown. We're seeing him really turn the corner. That's what young players (23) do. You have to give them time."
Puempel made it 3-1 at 8:30 of the third period when he picked up a rebound of a Patrick Wiercioch shot off the end boards and scored into the open side.
It was the seventh NHL game for the 24th pick in the 2011 NHL Draft.
Spooner's first goal was a shot from the right-wing circle that found its way through a crowd and deflected into the net off the far post.
Cameron said he was confident the Senators can bounce back.
"One thing this team has shown over the last little while is resilience," he said. "We've been down and counted out before. We're just going to focus on how to beat Montreal the next game.
"They're not showing me any signs they're not going to keep their nose to the grindstone and let the chips fall where they may."
The Bruins host the Tampa Bay Lightning on Thursday.