Hewitt, once ranked No. 1 in the world, recorded a 6-4, 6-3 victory that set up a semifinal meeting with Rajeev Ram.
Ram, a former winner of this event, surprised No. 2 seed Kei Nishikori 7-6 (8-6), 6-3 in their quarterfinal match.
In second-round action Thursday, Benjamin Becker ousted Milos Raonic 6-3, 6-3, and No. 6 seed Ryan Harrison defeated Jesse Levine 6-3, 6-4.
The other quarterfinals will be held Friday, with defending champion John Isner facing Izak Van der Merwe and Harrison taking on Becker.
Beyonce flaunts bikini body, Blue Ivy in vacation pics
Benedict Cumberbatch's dramatic reading of R. Kelly lyrics is just what you need