OKLAHOMA CITY —
Fellow All-Star Russell Westbrook had an off night, making 5 of 18 shots while scoring 14 points and passing out nine assists.
The Thunder's 21 turnovers led to 31 Atlanta points.
"I wish I could have had a couple of those turnovers back," said Durant, who has 20 assists and 16 turnovers in three games this season.
Oklahoma City pulled to 91-89 after Martin's 3-pointer from the left corner got the crowd roaring with 4:06 to play. Kendrick Perkins protested after being called for a foul for hacking Devin Harris on the arm on a baseline drive, and Harris hit both free throws.
On the next trip, Westbrook tried to save a rebound under the basket but ended up feeding Horford with a behind the back pass for a dunk. Another Horford dunk set up by Zaza Pachulia and Stevenson's 3-pointer — also off a Pachulia pass — bumped the lead to 100-91 with 1:28 to play.
That was too much for Oklahoma City to overcome.
Williams, the runner-up for Sixth Man of the Year last season with Philadelphia, was one of several acquisitions in an offseason roster shake-up that included Joe Johnson leaving for Brooklyn.
Martin, the Thunder's new sixth man after James Harden was dealt to Houston a week ago, got it going early with 22 first-half points. But it was Williams who finished it off.
"Lou got into a rhythm. He got into a rhythm and we were going to ride it," Drew said. "I had to make a decision whether to bring (starters) Jeff (Teague) and Kyle (Korver) back, but the group that was in there, they had a good rhythm going and I did not want to do anything to disrupt that.
"So, we decided to ride Lou's hot hand and he made some really big baskets," he added. "He made some really big plays for us."