Fourth seed Denis Istomin has advanced to the last eight of the Sydney International with a 7-6[5] 6-2 win over Russia's Dmitry Tursunov.
The Uzbek had to fend off seven break points and was pushed all the way in a tight first set, which he edged after taking it to a tie-breaker.
Istomin took both break-point opportunities that he managed to carve open to take the second set 6-2 in clinical fashion.
He will play Juan Martin del Potro, who beat Radek Stepanek in three sets, for a place in the semi-finals.
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