Martinook took a pass from Nikolaj Ehlers in the slot and beat a screened Linus Ullmark with a wrist shot that went in off the right post.
Martinook's goal came after Mark Jankowski thought he had won it for the Hurricanes during a delayed penalty at 17:18 of the first overtime. However, a review initiated by the Situation Room determined that the play was offside prior to the goal.
Despite the overturned goal, Martinook was still awarded a penalty shot for being hooked on a breakaway by Warren Foegele at 16:49. Martinook attempted to beat Ullmark with a shot from the slot, but the goaltender was able to get his glove on it.
Sebastian Aho and Logan Stankoven scored for the Hurricanes, who are the No. 1 seed from the Metropolitan Division and Eastern Conference. Frederik Andersen made 36 saves.
Drake Batherson and Dylan Cozens scored, and Jake Sanderson had two assists for the Senators, who are the second wild card from the Eastern Conference. Ullmark made 43 saves.
Carolina leads the best-of-7 series 2-0. Game 3 will be at Canadian Tire Centre in Ottawa on Thursday (7:30 p.m.; CBC, TVAS, SN, TBS, FDSNSO, HBO MAX).
Carolina scored on a power play to take a 1-0 lead at 6:31 of the first period. Taylor Hall sent a pass from behind the net out to Stankoven, who beat Ullmark five-hole with a one-timer from below the right hash marks.
Aho made it 2-0 at 7:50 of the second period. He intercepted the puck in the defensive zone and started a 2-on-1 rush with Jordan Staal as a penalty kill expired. The Hurricanes captain then skated into the right circle before sending a pass across to Aho, who tapped it past the outstretched right pad of Ullmark.
Batherson cut the lead to 2-1 at 10:47. Sanderson gloved down Aho's clearing attempt at the blue line and passed down to Batherson near the left post. Batherson's centering attempt for Claude Giroux hit off the skate of Carolina defenseman Jaccob Slavin and deflected right back to Senators forward, who quickly scored short side on Andersen.
Cozens tied it 2-2 at 16:40 of the second with a sharp-angled wrist shot from the bottom of the right circle that slipped through Andersen’s five-hole.
Ullmark pushed the game to overtime by making a crucial save with 22 seconds remaining in regulation. Ehlers sent a centering pass out front to Staal, whose one-timer from the edge of the crease was stopped by the flailing left shoulder of Ullmark.
