Harper had a poor shooting night (six-of-18), but continued to put the ball up.
"I knew if I kept shooting, they were going to start falling for me so luckily they fell when we needed it most," Harper explained.
Harper's five straight points, including a game-tying three-pointer sent the game to a second overtime.
Kevin Anderson filled in for the departed Maalik Wayns nicely, scoring 12 points and dishing out nine assists. Kyle O'Quinn (11) and DeAndre Liggins (11) also scored in double figures.
Clay Tucker led the 76ers with 15 points.