MEMPHIS - Australian Bernard Tomic fired nine aces past Alexandr Dolgopolov in ousting the fourth-seeded Ukranian 6-1, 7-5 on Thursday to reach the ATP Memphis Open quarter-finals. The German-born 22-year-old dispatched 23rd-ranked Dolgopolov in only 66 minutes to book a date in the final eight against Donald Young, who eliminated fellow American Denis Kudla 7-5, 6-3.

Tomic's win was the biggest upset of the $585,000 (512,000 euros) indoor hard-court event. Second-seeded South African Kevin Anderson advanced on cue Thursday with a brisk 6-3, 6-2 victory over Australian Sam Groth. Anderson set up a quarter-final meeting with sixth-seeded American Steve Johnson, who defeated Germany's Dustin Brown 4-6, 7-5, 7-6 (7/3).

Tomic, who ousted Dutchman Igor Sijsling in the first round, did not face a break point in ripping through the opening set and rescued seven of eight break-points against him in the second. "I played pretty good the first set," Tomic said. "After that was a roller-coaster, but I managed to stay in it and winning the second set was important. I was down a break 4-1. I said to myself, 'It's only one break. Stay in there and have a shot' and it worked for me."

Tomic, ranked 49th, improved to 3-5 all-time against Dolgopolov. He had won their most recent prior matchup in last year's Sydney quarter-finals and in a five-set battle in the third round of the 2012 Australian Open. Tomic has now reached the quarter-finals in three of his four tournaments in 2015.

"I'm focusing, I'm trying my best," he said. "I need to improve a lot -- I'm ready for that challenge." The other two quarter-finals were set on Wednesday. Two-time defending champion and top seed Kei Nishikori of Japan will take on American qualifier Austin Krajicek -- who toppled fifth-seeded Ivo Karlovic in the second round. And third-seeded American John Isner will face compatriot Sam Querrey.