Wallace had nine points in the first quarter and added a 3-pointer in the third as the Pistons, who never trailed, outscored the Wizards 19-11 to take a 57-47 lead entering the fourth. They extended their lead to 71-53 with 4 minutes to play.
It was Washington's last game in North America for 12 days. They are scheduled to leave on Saturday for a trip to Berlin and Barcelona, where they will play New Orleans on Oct. 14 and Oct. 17.
The Wizards were without Antawn Jamison, who bruised his right knee Monday against Dallas, and center Brendan Haywood, who will have surgery on his torn ligaments on his right wrist next week. They were also missing guard Juan Dixon (right calf) and swingman Nick Young (sore left knee).
Thomas, who missed last season after heart surgery, started at center and played 22 minutes in his most extended appearance this preseason. Andray Blatche, who started at forward in place of Jamison, fouled out in the third quarter after missing 10 of 12 shots from the field.