Steve Johnson pulled off another upset over one of the circuit's big men at the Citi Open in Washington on Thursday, ousting towering ninth seed Ivo Karlovic 3-6 7-6 7-6, while top-seeded Czech Tomas Berdych was also eliminated in the third round.
Johnson, who disposed of lofty fellow American and fifth seed John Isner on Wednesday, saved two match points against the 6ft-11in (2.11m) Karlovic and withstood a barrage of 27 aces to seal victory over the Croat in a third-set tie-breaker.
Wild card Berdych was broken four times as he succumbed to 24-year-old Canadian Vasek Pospisil 6-2 6-4 in only 81 minutes in the evening session at the William H.G. Fitzgerald Tennis Center.
Pospisil, who teamed up with American Jack Sock to win this year's Wimbledon men's doubles crown, booked his place in the last eight where he will face Santiago Giraldo of Colombia, a 6-2 6-0 winner over Victor Estrella of Dominican Republic.
Also going through to the quarter-finals on Thursday was big-serving Canadian Milos Raonic, who overpowered veteran Australian Lleyton Hewitt 7-6 7-6 in a match where neither player had their serve broken.
Raonic, the second seed, won 72 percent of the points on his serve while firing down 29 aces as he triumphed after a tightly contested encounter lasting a little less than two hours.
"I'm happy with a lot of things about the win today, especially the way I was able to fight through the important games," Raonic, 23, told reporters.
"I was able to find my rhythm well at the end of each set. He made it difficult for me. The right attitude really got me through today in the key moments."
World number seven Raonic will take on Johnson in the quarter-finals.
In other matches, fourth-seeded Japanese Kei Nishikori beat Slovalia's Lukas Lacko 6-2 2-6 6-3, sixth seed Richard Gasquet of France crushed American Tim Smyczek 6-3 6-2 and big-serving South African Kevin Anderson eased past Tunisia's Malek Jaziri 6-3 6-4.
In the women's competition, second-seeded Russian Ekaterina Makarova brushed aside American Lauren Davis 6-2 6-4 in the second round and fifth seed Anastasia Pavlyuchenkova of Russia eased past Japan's Hiroko Kuwata 6-3 6-3.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Greg Stutchbury)