Fifth-seeded Steve Johnson ended qualifier Ryan Harrison's season-best run in the Citi Open's third round, winning the all-American matchup 6-4, 6-4 on Thursday.

Johnson, a member of the U.S. Olympic team headed to Rio de Janeiro next month, broke Harrison once in each set, did not face a break point himself and ended the match with a 130 mph ace.

In the quarterfinals of the hard-court tournament, Johnson will face top-seeded John Isner or No. 15 Marcos Baghdatis. Last year, Isner beat Johnson in the Citi Open semifinals.

Also Thursday, No. 13 Ivo Karlovic hit 21 aces and eliminated No. 3 Bernard Tomic 7-6 (4), 6-3.

In women's action, third-seeded Monica Puig lost to Lauren Davis 6-4, 6-2, while fourth-seeded Kristina Mladenovic beat 2013 Wimbledon runner-up Sabine Lisicki 6-3, 6-3.