Wittenberg shot a bogey-free 63.
Gangjee, who has been having an average season, started birdie-birdie from the 10th and then bogeyed the 13th. He birdied the 14th and 18th to turn in three-under 33.
On the back nine, the front half of the course he birdied the third but just as he neared the finish, he dropped a shot on the eighth to finish at 68.
Gangjee's best this year has been tied 16th at the TPC Stonebrae Championships and has made three cuts in eight starts before this week.
Wittenberg, who was paired with Tiger Woods in the last round and ended tied 10th at the US Open last week, was two clear of Kevin Johnson and Jason Gore. Wittenberg already has one win on the Nationwide Tour this year.