"I think we were pretty fortunate tonight," said Rochester coach Randy Cunneyworth, who saw his team rally from a two-goal deficit in the third period before Smith's game-winner at 2:35 of the extra frame.
"We're not in our position by accident, though. We've got a lot of confidence in our group as a whole, and we can score by committee."
That was evident as five different players beat Toronto netminder Justin Pogge, and three Amerks had two-point games. Forwards Rob Globke, Kamil Kreps, Anthony Stewart and Marek Zagrapan also scored for Rochester, with Globke, Kreps and Stewart each collecting an assist as well.
Right winger Ben Ondrus scored two power-play goals for the Marlies, while forwards Erik Westrum and John Mitchell added singles in front of 2,877 fans at Ricoh Coliseum.
Toronto centre Kris Newbury picked up two assists.
"You think you deserve better, but it doesn't always happen that way," said Marlies coach Greg Gilbert. "Rochester is at the top of the league for a reason. They never quit.
"But I feel we gave them a few opportunities, with some turnovers, and a team like that is going to capitalize on mistakes."
Rochester improved to 16-2-1 to secure its lead atop the Western Conference, while Toronto fell to 7-10-3.
"We've got to keep going and bear down when we do get opportunities," said Gilbert, whose club came out flying in the first period with several scoring chances. "It's a learned skill to be a goal-scorer, you've got to work at it. It's not as though (the Marlies) aren't trying."
Both teams were playing their third game in three nights; it was also the Amerks' fourth contest in five days.
Rochester netminder Craig Anderson stopped 33 of 37 shots for the victory. At the other end, Pogge made 35 saves on 40 shots.
"He's 20 years old, he's fresh out of junior, he's playing against men, players who are faster and can shoot the puck harder," said Gilbert when asked to evaluate Pogge's performance. "He's working hard and getting better."
The Marlies were 2-for-4 on the power play, while the Amerks went 0-for-4 with the man advantage.
The Marlies led 2-1 after the first period and 3-2 through 40 minutes. Toronto scored early in the third period to build a two-goal cushion, but the Amerks rallied with a pair of markers in the middle of the frame to force overtime.
Westrum opened the scoring with a goal midway through the first period, when his shot from a bad angle in the right corner went in off of Anderson at 9:37. Ondrus made it 2-0, on the power play, when he redirected Newbury's centring pass at 16:02.
Globke put the Amerks on the board when he swooped in from the right wing and whipped a backhander past Pogge at 18:36 of the first period.
Ondrus gave Toronto another two-goal cushion with his second man-advantage marker of the game at 6:27 of the second period. Rochester's Kamil Kreps pulled the Amerks within a goal late in the middle frame when he pounced on a rebound in the slot and one-timed the puck through Pogge at 19:52.
Mitchell snapped a wrist shot between Anderson and the left goal post at 1:14 of the third period to give Toronto its third two-goal bulge in the game, but Stewart scored at 9:27 and Zagrapan, with his first professional goal, tied it at 4-4 when he deflected a shot from the point past Pogge.
Smith finished off the comeback when he corralled a loose puck at the left point and fired a low slapshot that somehow eluded Pogge.
The Marlies' next game is at home against the Milwaukee Admirals on Wednesday.
Notes: Rochester entered last night's contest with just two regulation-time defeats, and the Amerks were shut out both times: a 5-0 loss at Syracuse Oct. 27 and a 6-0 defeat in Hamilton on Saturday night ... The Marlies were without several players due to injuries, including defencemen Brad Brown (back) and Dominic D'Amour (ankle) and forwards Jeremy Williams (knee) and Brad Leeb (back). Leeb may be back this week, while the others are expected to be sidelined longer ... Defenceman Jay Harrison, who began the season with NHL parent Toronto Maple Leafs but has been with the Marlies on a two-week conditioning assignment since Nov. 15, didn't dress for the second consecutive game. According to Marlies PR staff, Harrison will be placed on waivers by the Maple Leafs today ... players can't be waived on Sundays and, if no other NHL team claims him, he'll become Marlies property on Tuesday ... The Amerks also played without several regulars. Forwards Drew Stafford, Dan Paille and Michael Ryan and defenceman Mike Funk are up with parent Buffalo as the Sabres battle injuries, and centre Drew Larman was recalled by the Florida Panthers.