"There were periods of the game where we felt really good about the way we were playing, but that being said, I think there were parts where we got away from our game plan a little bit," Rielly said. "For the most part, there were some good things that happened, and the end result was obviously what you want."
Rielly finished a give-and-go with Zach Hyman at the top of the crease after the Senators scored two straight goals early in the period to tie the game 4-4.
[WATCH: All Senators vs. Maple Leafs highlights]
"[Rielly] made a great play skating and then got it to me," Hyman said. "I just wanted to try to be like [Mitchell Marner] there. … I was just trying to get it backdoor, and it's good [Rielly] was there and he put it in. I didn't really think about it too much. I just wanted to put it in a space for him, he was driving hard."
Hyman and John Tavares each had a goal and an assist, Andreas Johnsson and Auston Matthews scored, and Marner had two assists for the Maple Leafs (33-17-3), who have won three games in a row. Frederik Andersen made 39 saves.
Magnus Paajarvi scored two goals, Matt Duchene and Thomas Chabot scored, and Jean-Gabriel Pageau had two assists for the Senators (19-29-5), who have lost five straight. Craig Anderson made 25 saves.
"I thought we had momentum for a good portion of the game, but we made a couple mistakes and they made us pay, and that was all the momentum they needed," Anderson said. "We came out flying in the third, got it back to 4-4, but we made a couple mistakes and they made good on their chances."
Matthews gave the Maple Leafs a 3-2 lead at 16:29 of the second period when he got around Senators defenseman Mark Borowiecki in the slot and shot past a sprawled Anderson. It was his fourth goal in the past five games following a seven-game drought.
Video: OTT@TOR: Matthews digs puck out, beats Anderson
Tavares scored his Toronto-leading 32nd goal at 18:20 to make it 4-2 when he redirected a pass from Marner at the left side of the net.
Chabot got Ottawa to within 4-3 when he scored 40 seconds into the third period, and Paajarvi tied it 4-4 at 3:59 with his second of the game.
"The bottom line is I thought we were really ready to play. … I thought we were playing well," Maple Leafs coach Mike Babcock said. "Then we just got careless and we never really seemed to be able to get it back. At the same time, when you're a good team, you win games sometimes that aren't very pretty, but you still won."
Hyman put Toronto up 1-0 at 7:46 of the first period when he redirected a pass from Marner at the top of the crease.
Video: OTT@TOR: Hyman buries feed from Marner
Paajarvi tied it 1-1 at 17:18 when he took a pass from Pageau at the blue line, skated into the slot, and shot past Andersen's glove.
Duchene scored at 1:35 of the second period to give the Senators a 2-1 lead, but Johnsson tied it 2-2 at 14:20.
"They've got great offensive threats, they can make some good plays and good passes," Anderson said. "It's one of those things where you need to play tight on them, not give them time and space, because when they do (have it), they can make some great plays. Hats off to them, but we have to be a little bit tighter. We had plenty of chances to score, we had four (goals) tonight, so that should be definitely enough, but the mistakes we had tonight were self-inflicted."
Video: OTT@TOR: Duchene lifts shot over sprawling Andersen
Rielly's goal gives him 53 points (14 goals, 39 assists) this season, a new NHL career high.
"It's not something I was really thinking about until just now," he said. "We've got lots of hockey left, lots of important games down the stretch. There are more important things to be thinking about."
They said it
"Obviously, we're not happy with our mistakes, but at the end of the day, we were playing a very solid team and we feel like we could have won, we feel like we played well. They're a very talented team, a Stanley Cup contender, and obviously to play well like that against them, it can be a positive for us." -- Senators defenseman Thomas Chabot
"I think he [is appreciated] around here. He's a great player, he's a big part of this team and plays a lot of minutes. He plays on the [penalty kill], he's a huge part of this team and we're very lucky to have a player like that." -- Maple Leafs defenseman Morgan Rielly on forward Zach Hyman
Need to know
Maple Leafs defenseman Jake Muzzin played his 500th NHL game. He has 216 points (52 goals, 164 assists) in his career. … Rielly had 52 points (six goals, 46 assists) last season. ... Chabot, who is tied for eighth among NHL defensemen with 40 points, was kept off the score sheet in the previous five games.
Senators: Host the Anaheim Ducks on Thursday (7:30 p.m. ET; RDS2, TSN5, KCOP-13, NHL.TV)
Maple Leafs: At the Montreal Canadiens on Saturday (7 p.m. ET; CBC, SN1, CITY, TVAS, NHL.TV)
Video: Maple Leafs top Senators for fourth straight home win