Mike Gartner has scored 652 regular-season and playoff goals in a 15-year NHL career.
"It's the biggest one so far," Gartner said after his goal at 8:53 of overtime provided a season-saving victory.
Gartner's shot came from the side of the San Jose net after a pass from behind the net from Doug Gilmour. It forced a seventh and deciding game Saturday night in the Western Conference semifinal series.
"I went to the side of the net and Dougie made a great play behind the net to get me the puck," Gartner said. "I slid a shot into the crease and it hit (goaltender Artur) Irbe's skate and went in.
"It couldn't be called a pretty goal, but it looked pretty from my angle."
Wendel Clark scored Toronto's other two goals.
Igor Larionov and Jeff Norton scored for the Sharks.
San Jose forward Johan Garpenlov came within an inch of ending the game when he whistled a shot off a post 73 seconds into overtime.
"You never know what's going to happen in overtime," Shark Coach Kevin Constantine said. "We had a couple of chances and didn't make it.
"They had a chance and they scored. That's the way it goes. . . . Toronto's a good team. Nobody thought this would be easy."
The Sharks, with the worst regular-season record in the playoff field, pushed the Maple Leafs to the limit.
"We didn't count on putting ourselves in a position where overtime would be needed," Gartner said. "It's a great sense of relief to win.
"A goal the other way would have ended our season."