Toronto jumped out to a 3-0 lead in the first 12 minutes and rarely looked back. Marner's second goal was the 100th point of his young National Hockey League career.
Patrick Marleau provided an empty-net goal and two assists while Auston Matthews, James van Riemsdyk and Nazem Kadri also scored as the Leafs posted their third straight win and eighth in the past 11. Toronto goaltender Frederik Andersen stopped 22 of 25 shots for his 27th victory of the season.
Johnny Oduya, Derick Brassard and Ryan Dzingel tallied for Ottawa as the Senators suffered their 19th loss in 26 games away from home.
Earlier in the week, Senators owner Eugene Melnyk indicated that changes are likely as the NHL trade deadline approaches. But players who are hoping to stay in Canada's capital did little to enhance their job security.
Marner opened the scoring with an unassisted goal 1:55 into the game as he circled into the slot and put home a high shot. Matthews put the Leafs ahead 2-0 seven and a half minutes later, converting a pass from William Nylander.
Marner's second goal came at 11:30 of the first period as he fired in a pass from Marleau, sending the Leafs ahead 3-0.
After the goal, Ottawa starting netminder Craig Anderson was pulled. He posted seven saves on 10 shots before being replaced by Mike Condon, who stopped 28 of 30 shots as the Sens were outshot 41-25.
Oduya put the Sens on the scoreboard midway through the second period as he whipped a slapshot over Andersen's catching glove.
Toronto went ahead 4-1 just over five minutes later with Van Riemsdyk putting a puck in off an Ottawa defender.
Brassard, back in the Senators lineup after missing two games with an undisclosed health issue, reduced Toronto's lead to 4-2 only 45 seconds into the third period. Defenseman Dion Phaneuf, a former Toronto captain, put in a shot off Brassard's knee.
But Kadri restored Toronto's three-goal lead less than two minutes later, working a give-and-go with Marner after the two Leafs forced a turnover in Ottawa's end.
Dzingel brought the Sens a shade closer at 13:32 of the final frame before Marleau closed out the scoring on a pass from Marner with Condon pulled for an extra attacker.
--Field Level Media
Ottawa | Toronto | |
Mark Stone 2 | Points | Mitchell Marner 5 |
Derick Brassard 1 | Goals | Mitchell Marner 2 |
Mark Stone 2 | Assists | Mitchell Marner 3 |
N/A | Power Play Goals | James van Riemsdyk 1 |
N/A | Short Handed Goals | N/A |
Mike Condon .933 | Save Percentage | Frederik Andersen .880 |
Mike Condon 28 | Saves | Frederik Andersen 22 |
Team | Shots | Goals | Power Play | Penalty Kill | Penalty Mins | Face Offs Won |
Ottawa | 25 | 3 | 0-2 | 4-5 | 10 | 28 |
Toronto | 41 | 6 | 1-5 | 2-2 | 4 | 31 |