Green scored 22 points and Harris had 21 for La Salle, which will play second-seeded Temple (18-12) in the quarterfinals on Thursday. The Owls crushed the Explorers 85-66 on Saturday.
Reggie Jackson had a career-high 29 points for 10th-seeded Duquesne (17-13), which had a 72-65 with less than six minutes to play.
La Salle used 9-2 spurt to tie the game at 74 on a shot in the lane by Jerrell Williams with 2:36 to play. And a jumper by Shawn James of Duquesne and two free throws by Harris tied the game at 76.
Jackson, whose previous high of 25 came against Temple last week, nailed a 3-pointer for a 79-76 lead with 1:47 to play.
Green was called for a charge on La Salle's next possession, but Jackson lost control of the ball on a drive to the basket.
After calling a time out to call a play, Harris launched a 3-pointer from almost in front of his coach sitting on the bench to tie the game with 57.2 seconds to go.
Jackson had another turnover on Duquesne's next possession, and Green was later fouled in the lane. He missed the first free throw and made the second.
Kojo Mensah and Kieron Achara had a mix-up on Duquesne's next possession and Mensah's pass went out of bounds in front of his own bench.
Guillandeaux was fouled and made his free throws and Tucker could not convert his last 3-point shot with about :04 to play. Duquesne got the rebound but it could not get off another shot.
