The Sixers were trailing 98-88 with 2:10 to play and forced overtime with a 14-4 run that featured three 3-pointers from Hawes, including a fall-away at the end of regulation. Hawes also had 12 rebounds.
Philadelphia took the lead on the first basket of overtime and never gave it up, extending Milwaukee's losing streak to seven games.
Caron Butler scored 38 points for the Bucks, falling two points shy of his career high on 13-of-22 shooting from the floor. He was 4 of 8 from beyond the arc.
Only two other Bucks, Ersan Ilyasova (19) and Gary Neal (10) finished in double figures.
The Sixers led by as many as 15 points in the second quarter, but the Bucks scored 23 of the final 31 points in the period to get within 55-53 at the break.
Neither team led by more than four points in the fourth quarter before the Bucks stretched their lead to 10 with just over two minutes to play and appeared ready to end their losing streak.
NOTES: Sixers second-year guard Tony Wroten left the game in the second half with a lower-back strain and did not return. ... Forward Thaddeus Young missed his second straight game while on leave from the Sixers for personal reasons. ... Bucks G Brandon Knight missed his fifth straight game with a hamstring injury.