Pominville scored twice in the first period, the first a power-play goal on a near-perfect pass from Roy. Roy took a pass from Toni Lydman and executed a one-touch feed to Pominville in the center for the easy goal.
"It was a great play," Pominville said. "I was surprised he one-touched it right away and I had a lot of net to shoot at."
He scored his second goal of the period on a follow up after Antero Nittymaki turned away his initial shot on a breakaway.
Defensemen Tyler Myers added his 10th goal of the season as the Sabres took a 3-0 lead into the first intermission.
Buffalo (37-22-10) extended its lead in the Northeast Division to five points over Ottawa, a 6-3 loser at Atlanta on Thursday night.
Tampa Bay (28-30-12) has watched its playoff hopes evaporate during this home stand with its third loss in a row. The Lightning have scored four goals during that span.
"With every game there's pressure to win," Tampa Bay coach Rick Tocchet said. "Some people just get wound up, sometimes you get too wound up and to me, it looked like anytime Buffalo wanted the puck they got it. We were just really nervous."
They were able to generate the games first scoring opportunity as Steve Downie had a good look at an open net but missed the shot wide. Tampa Bay also had three power-play opportunities in the first period but failed to score as they were outshot 14-4.
"You've got to set the tone for the night," Miller said. "It's not going to be about the other team running around. It's going to be about we want to do."
Downie and Lecavalier had third-period goals for Tampa Bay, but Vanek scored an empty-net goal and Pominville added his third with 34 seconds remaining.
Steven Stamkos had two assists for the Lightning, giving him 42 goals and 40 assists. ... Craig Rivet was given a 10-minute game misconduct for instigating a fight with Lightning forward Todd Fedoruk at 2:07 in the first period.
Copyright by STATS LLC and The Associated Press
Arena: Amalie Arena Location: Tampa, Florida
Referees: Brian Pochmara, Chris Rooney Linesmen: Greg Devorski, Brad Lazarowich
Attendance: 16,868 (87.8% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Jason Pominville (19)
(Power Play) Assists: Derek Roy, Toni Lydman
Tyler Myers (10)
Assist: Jochen Hecht
Jason Pominville (20)
Assist: Henrik Tallinder
Derek Roy (19)
Steve Downie (18)
Assists: Steven Stamkos, Martin St. Louis
Vincent Lecavalier (21)
(Power Play) Assists: Steven Stamkos, Teddy Purcell
Thomas Vanek (23)
(Empty Net) Assist: Derek Roy
Jason Pominville (21)
Assists: Tim Connolly, Toni Lydman