Alonzo Nelson-Ododa tacked on 13 points for seventh-seed Richmond (19-13), which will battle second-seed VCU in Friday's quarterfinals.
Ovie Soko posted 23 points and 13 rebounds for 10th-seed Duquesne (13-17). Dominique McKoy and L.G. Gill each chipped in 10 points.
At the end of the first half the Spiders led 32-26. They connected on only 38.5 percent from the floor in the period, but limited the Dukes to 37.9 percent shooting, while netting 5-of-12 from 3-point range and 7-of-7 at the free-throw line.
Richmond improved to 53.6 percent shooting over the final 20 minutes to pull away for the win. Duquesne also hit a better percentage from the floor (.457), but it wasn't enough.
The Spiders enjoyed a 40-34 advantage on the glass. They also made more free- throws (18) than the Dukes attempted (eight).