Krejci played 16:42 and scored his sixth goal of the season.
"I thought he was very good, lots of pace, good composure, dancing through the neutral zone, making plays, so it was nice to have him back and healthy," Boston coach Bruce Cassidy said. "Let's hope it stays that way. He's had his fair share of tough luck this year, and hopefully he can stay healthy because he makes us a better team."
The Bruins went 3-for-4 on the power play. Spooner scored to make it 1-0 with the man-advantage at 8:13 of the first period on a rebound of a shot by Krejci that was tipped to him by David Backes.
Acciari scored on a backhand at 3:29 of the second period to make it 2-0, and Spooner scored on a breakaway at 5:38 to make it 3-0.
Krejci scored a power-play goal from beside the left post at 13:39 of the second period, and Bergeron scored one on a tip at 1:11 of the third.
"There's not much to say. They were the better team from start to finish," Senators captain Erik Karlsson said. "They did a lot of good things and we didn't do a good job eliminating the things they did well. We gave them a little bit too much. Overall, they were the better team."