Thomas, playing his first game after undergoing offseason hip surgery, allowed four goals on 15 shots.
Tyler Seguin, the second pick in the June draft, played his first game as a center for the Bruins and didn't have a point. He had a goal and an assist in two previous games as a wing.
The Bruins left after the game for Belfast, Northern Ireland, where they will train for two days before playing an exhibition game. Then they move on to Prague for their final preseason game and open the season there with two games against the Phoenix Coyotes, Oct. 9 and 10.
Copyright by STATS LLC and The Associated Press
Arena: TD Garden Location: Boston, Massachusetts
Referees: David Banfield, Wes McCauley Linesmen: Brian Murphy, Michel Cormier
Attendance: 14,916 (84.9% full)
Nicklas Backstrom 1 Assist: Jason Chimera
Nicklas Backstrom 2 Assist: Jeff Schultz, John Carlson
Andrew Gordon 1 Assist: Tyler Sloan, Jason Chimera
Matt Bradley 1 Assist: Boyd Gordon
Mark Recchi 1 (power play) Assist: Patrice Bergeron, Michael Ryder