The goal by Pominville was the first for Florida since Derek Roy had tallied with 2:10 remaining in the opening period.
Florida, which leads the Southeast Division by six points over Washington, lost in overtime for the fifth time this season -- tied for third-most in the NHL behind Montreal (7) and the New York Islanders (6).
The Panthers had been trying for their 11th road victory of the year, which would have broken a tie with Philadelphia for most in the league.
Florida's only goal came from Jason Garrison on the power play in the second period.
Ryan Miller made 22 saves for the Sabres. It was his first win since returning from an injury that cost him three weeks of action.
Scott Clemmensen, who had won in his only other three appearances this season, stopped 18-of-20 shots.