Marner cut it to 3-2 at 19:37 on a backdoor tap-in off a pass from Rielly.
"If there's a positive out of the game, it's you're down 3-1 and you find a way to come back and get a point and give yourself a chance to get the second point," Keefe said. "We had some opportunities there in the third period to go ahead in the game, but we couldn't get it in."
Auston Matthews tied it 3-3 at 5:38 of the third period with a power-play goal from the high slot.
"I just don't think we've really put together a full 60-minute game," Matthews said. "I think that consistency within the game and momentum shifts are kind of hurting us right now."
NOTES: Couture has 640 points (300 goals, 340 assists) in 855 games in 14 NHL seasons, all with the Sharks. He is their third player to score 300 goals (Patrick Marleau, 522; Joe Pavelski, 355). … Maple Leafs forward William Nylander had his five-game point streak end (three goals, two assists). … Matthews' goal was his 261st to pass Wendel Clark for eighth in Maple Leafs history. … San Jose went 2-for-3 on the power play after going 2-for-27 (7.4 percent) the first nine games. Toronto went 1-for-4, only the second power-play goal the Sharks have allowed this season (28-for-30, 93.3 percent).