Buffalo's NHL-best 10-game winning streak ended in a 5-4 loss in Tampa on Thursday, and Barkov eluded Jack Eichel, positioned himself in front of the Buffalo goal in overtime, and buried his ninth goal off a pass from Jonathan Huberdeau to hand the Sabres consecutive losses for the first time in November.
Florida also had goals from Jared McCann and Evgenii Dadonov, and Huberdeau had two assists. The Panthers won their sixth straight against Buffalo.
Jeff Skinner and Sam Reinhart scored goals for Buffalo, which finished November with an 11-3-1 record.
Reinhart added an assist for a two-point night, and Eichel had two helpers.
Florida goalie James Reimer made his fifth straight start and stopped 22 shots. Buffalo's Linus Ullmark made 40 saves and also recorded his first career assist on Reinhart's goal.
Reinhart led a 2-on-1 break with Skinner and only Florida's Keith Yandle back to defend. Skinner roofed a clean pass from Reinhart over Reimer for his team-leading 20th goal and 12th on the road.
Skinner's marker broke a second-place tie with Boston's David Pastrnak among NHL leaders in total goals. The Buffalo left winger trails Winnipeg's Patrik Laine by one.
McCann tied it 1-1 at 18:31 when his one-timer from the right circle hit the stick of Sabres defenseman Zach Bogosian and went over Ullmark for a power-play goal. McCann's tally was his fifth this season and third in the last four games.
Florida's power play ranks second overall in November, and the Panthers have scored man-advantage goals in 14 of their last 15 games.
Reinhart took a pass from Eichel and chipped in his sixth goal at 2:41 of the second period on Buffalo's first power play for a 2-1 lead.
Dadonov scored the Panthers' second power-play goal just eight seconds after Casey Nelson went off for high-sticking, knotting the game 2-2 with his 11th goal at 11:56 of the third period.
(With inputs from agencies.)