Kohlschreiber fought off five of six break points he faced in a 7-5, 6-2 win over German countryman Nils Langer. Kohlschreiber finished with a pair of breaks in each set.
He'll go against Gael Monfils in the quarterfinals after Monfils ran past sixth-seeded Florian Mayer 6-3, 6-0 in 54 minutes. One of the games Monfils lost came on a break but he won 70 percent of all the points in the second set.
The other quarterfinal set Wednesday has wild-card entrant Michael Berrer, another German, playing Roberto Bautista-Agut.
Berrer earned his berth with a 6-2, 6-7 (1-7), 6-3 win over third-seeded Jeremy Chardy. Berrer didn't lose his serve in the match. Bautista-Agut eliminated No. 8-seeded Martin Klizan 6-7 (3-7), 6-1, 6-4 with five breaks over the second and third sets.