Drake Batherson, Artem Zub and Claude Giroux scored for the Senators (42-27-10), who have won three straight and four of their past five. Jake Sanderson had two assists, and Linus Ullmark made 21 saves.
Thomas Chabot returned to the lineup after breaking his right arm in a 2-1 win at the New York Rangers on March 23. Chabot had surgery March 26 and missed eight games after he was initially expected to be out 4-8 weeks.
Jesper Boqvist scored the lone goal for the Panthers (37-38-4), who have lost four in a row (0-3-1). Sergei Bobrovsky made 22 saves.
Batherson gave the Senators a 1-0 lead while on a power play at 6:49 of the first period. He set up in front of the net and deflected Sanderson's one-timer from between the circles to the short side.
Zetterlund made it 2-0 at 17:00. Lars Eller won a board battle and fed Zetterlund in the right circle, where he roofed a wrist shot over Bobrovsky's glove that bounced quickly off the back bar.
Zub increased the lead to 3-0 at 3:03 of the third period, beating Bobrovsky with a snap shot inside the left post from the right circle after Sanderson's initial shot caromed back off the end glass.
Boqvist cut the deficit to 3-1 with a snap shot from the shot that trickled through Ullmark's pads at 14:17.
Giroux scored an empty-net goal at 16:43 to make it 4-1, and Zetterlund scored his second goal through the five-hole just 19 seconds later at 17:02 for the 5-1 final.
