Wawrinka, the top seed for the tournament, easily handled Benjamin Becker 6-3, 6-1 in 54 minutes.
Wawrinka saved all four of Becker's break chances while finishing off half of his eight opportunities. He won more than three-quarters of the points when serving, including 86 percent when getting his first serve in.
He'll go against Aljaz Bedene in the quarterfinals. Bedene dropped the first set 1-6 but was up in the second 3-0 over Alexander Kudryavtsev when Kudryavtsev retired.
No. 7-seeded Edouard Roger-Vasselin beat Jiri Vesely 6-4, 6-4 by saving eight break points and will play Sela in the semifinals.