This will be the first semifinal for the Australian since 2010, when he went on to win the title in Halle, defeating the Swiss Federer in the final.
Hewitt, who dropped to 233 in the rankings, needed 1 hour and 18 minutes as he broke his opponent five times to sail to a comfortable victory, showing flashes of his very best when being at the top a few years ago.
He will now play American Rajeev Ram, who posted a superb victory over the second seed Kei Nishikori of Japan, beating him 7-6 (6) 6-3.
Ram, who reached the doubles quarterfinals at this year’s Wimbledon, has got great memories from this tournament as he defeated Sam Querrey in the 2009 final, winning his first ATP title.
For the other two semifinal spots, top seed John Isner will play South African qualifier Izak Van Der Merwe and German Benjamin Becker will meet American wild card holder Ryan Harrison.
It was Becker, who surprised the tennis experts after eliminating third seed Milos Raonic 6-3 6-3 in the previous round.