Grigor Dimitrov beat third-seeded Dominic Thiem 6-4, 6-4, 6-0 to reach the quarterfinals of the Australian Open for the fourth time.
The No. 18-seeded Dimitrov was down a break in each of the first two sets but rallied to keep up the pressure on his tiring opponent.
Thiem won the U.S. Open and was the runner-up at the Australian Open last year, but he was coming off a tough third-round match when he had to rally from two sets down to beat local favorite Nick Kyrgios in five.
Dimitrov, who has a career-high ranking of No. 3, will next play 114-ranked Aslan Karatsev, who upset Felix Auger-Aliassime to become the first man since 1996 to reach the quarterfinals on his Grand Slam debut.
The 27-year-old Russian qualifier dropped the first two sets but lifted his level and cut down his error-rate to beat the 20th-seeded Auger-Aliassime in five.