Third-seeded Sam Querrey beat Lleyton Hewitt 7-6 (6), 1-6, 7-6 (4) on Thursday to reach the SAP Open quarterfinals.
Hewitt, the former top-ranked player in the world, double-faulted twice in the third-set tiebreaker, including match point. The Australian has 28 career titles, and beat Querrey in two previous meetings.
Colombia's Alejandro Falla reached his first quarterfinal of the season, knocking off seventh-seeded Marinko Matosevic of Australia 6-4, 6-4.
In other matches, sixth-seeded Denis Istomin of Uzbekistan topped Germany's Benjamin Becker 6-3, 6-7 (5), 6-2; Belgium's Xavier Malisse, seeded eighth, squeezed past Australia's Matthew Ebden 5-7, 7-5, 7-6 (1) in a match that lasted almost 2 1/2 hours.
American Steve Johnson reached his first career quarterfinal with a 6-3, 6-3 victory over American qualifier Tim Smyczek.