Sijsling, of Amsterdam, ousted seventh-seeded Mikhail Youzhny 6-2, 6-2 by winning nearly half -- 36-of-73 -- of the points off Youzhny's serve. Sijsling had 12 break chances and was able to finish off four of them.
He avenged a loss to Youzhny last week in Croatia, in the first career meeting between Sijsling and Youzhny.
No. 8-seeded Grigor Dimitrov got by Dmitry Tursunov 6-2, 1-6, 6-4. He had 14 break opportunities, with eight of them coming in the decisive third set. Dimitrov had two breaks in that set to advance.
Marin Cilic, who won the tournament in Croatia last week, defeated Lukas Rosol 6-2, 6-2 in 60 minutes. Cilic won more than 70 percent of the points on serve and saved the only break point he faced.
Also Tuesday, Ernests Gulbis topped Denis Istomin 6-4, 7-6 (7-5) with three breaks and Jerzy Janowicz used the only breaks of the second and third sets to rally for a 3-6, 6-4, 6-4 win over Julien Benneteau.
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