OTTAWA -- Playing mainly for pride, the Toronto Maple Leafs made quick work of their provincial rivals to claim bragging rights in Ontario.
The Maple Leafs won four of six against the Senators to claim the season series.
Kessel beat Brian Elliott for his fourth goal in four games 11:20 in. Mitchell made it 2-0 when he scored 4:33 into the second. His goal had not even been announced when Grabovski increased the lead to 3-0 with his ninth goal at 4:52.
Jonas Gustavsson stopped 30 shots for the Maple Leafs, who are last overall in the Eastern Conference with 60 points but have won four of five.
"Everyone cares about everyone here," Kessel said. "We're playing for each other in here and we're trying to get some wins."
Rickard Wallin scored into an empty net for the Maple Leafs, who began their current 5-2 run with a 2-1 shootout win in Ottawa on March 6.
"When we were up three goals, I know I can let one in and we're still going to win the game so that feels good and of course that helps me a lot, too," said Gustavsson, who has won four in a row, a personal streak that began with Toronto's win 10 days earlier at Scotiabank Place.
Andy Sutton scored his first Ottawa goal late in the second. Elliott stopped 26 shots for the Senators, who lost their third in a row. Ottawa, which lost its last two games of a three-game trip to western Canada, has gone 1-5-1 since the Olympic break.
The Senators remain in fifth place overall in the East with 79 points, though Montreal is now just one point back following the Canadiens' 3-1 road win over the New York Rangers.
"I think we are struggling with handling the puck and making good passes and managing the puck," said captain Daniel Alfredsson, who got a boarding minor in the third for pushing Francois Beauchemin from behind along the boards. "It seems like when we get it we want to get rid of it right away instead of sometimes settling down and controlling the play. We're stretching at times and putting ourselves in difficult spots."
Kessel teammed up with linemates Tyler Bozak and Nikolai Kulemin to open the scoring. Kulemin took Bozak's pass in his own zone and rushed the puck to the left side of Ottawa's zone before feeding to the slot, where Kessel snapped a shot into the top right corner.
Mitchell made it 2-0 in the second when he sped past Sutton's attempt to check him into the boards along the right side before beating Elliott with a wrist shot for his fifth goal at 4:33.
The Maple Leafs increased their lead to 3-0 when Grabovski scored his second goal in his last three games. Grabovski he finished off Luca Caputi's centering pass at 4:52 after the Toronto rookie stripped the puck off Senators defenseman Erik Karlsson behind the net.
Gustavsson made a fine save on Chris Kelly's short-handed chance from the slot midway through the second but lost his shutout bid late in the middle period.
Sutton, who was acquired in a trade with the New York Islanders on Mar. 2, scored his fifth goal of the season -- his first in six games with the Senators -- with 1:34 left in the second to draw Ottawa within two.
Senators C Mike Fisher took part in the pregame skate but was left out of the lineup because of an upper-body injury. ... Ottawa D Filip Kuba (lower-body injury) missed his sixth straight game. RW Shean Donovan was a healthy scratch.