The Lighting won for the fifth time in seven games. Tampa Bay's 11 points are the most in the Eastern Conference.
Stamkos scored the last of Tampa Bay's three first-period goals with 2:10 left in the stanza, gave the Lightning a 4-1 lead with 2:38 left in the second and added an empty-net goal with 32 seconds to go in the third.
He ran his early-season goal total to eight, tops in the NHL. Smith improved his record to 4-0 even though he gave up 13 goals in his first three wins.
Chris Mason allowed three goals on 16 shots for the Thrashers and was replaced after one period by Peter Mannino, who stopped all but one of 16 shots.