Serge Ibaka supplied a 16-point, 12-rebound double-double and ignited an important fourth-quarter surge for the Thunder, who have won five straight games and seven of their last eight.
D.J. Augustin and Enes Kanter, who were acquired by Oklahoma City at the trade deadline on Thursday, netted 12 and 10 points, respectively, in their debuts. Kanter also had 13 rebounds.
After Williams' technical free throw tied the game at 94-94 with 6:19 to play, Ibaka's consecutive baskets kicked off a 10-2 run that gave the Thunder a 104-96 lead.
Augustin sealed the win with a trey that gave Oklahoma City a nine-point advantage with under three minutes to play.
Charlotte led 30-28 after 12 minutes of play, but the visitors closed out the half on a 6-2 spurt to take a 59-56 edge into the break.
The Thunder maintained their three-point lead as they led 86-83 heading into the final quarter.
Thunder star forward Kevin Durant was out due to a sore right foot ... Oklahoma City outrebounded Charlotte, 59-41 ... Kyle Singler supplied six points in his first game with the Thunder ... There were 12 lead changes and eight ties.