The Sabres beat Joseph four times on 20 shots, taking some of the luster away from his overtime victory against Atlanta Tuesday -- his 450th NHL win, but just his first since April.
The 41-year-old backup goaltender is filling in for Vesa Toskala, who gave up 14 goals in a three-game span last week.
After a scoreless first period, Pominville produced a power-play goal 6:50 into the second period and Roy scored on a tip-in less than three minutes later.
Pominville added an unassisted goal with 8:31 to play in the second and Roy tacked on a power-play goal early in the third.
Ryan Miller stopped 27 shots and lost his bid for a shutout at 8:29 of the third when John Mitchell got the best of him with a slapshot.