Del Potro books quarter-final clash with Querrey

Miami - Juan Martin Del Potro turned back a challenge by Damir Dzumhur on Thursday to book a quarter-final clash with defending champion Sam Querrey at the ATP Delray Beach Open.

Argentina's Del Potro, the 2011 Delray Beach champion playing just his second match of 2017, held on to beat the 24-year-old Bosnian 7-6 (7/5), 4-6, 6-3.

Del Potro fired a backhand return wide to miss his first chance to seal the match, Dzumhur holding to make it 5-3 in the third.

Del Potro gained another chance with a forehand crosscourt winner and secured the win when Dzumhur, scrambling back to defend a lob, missed a desperation between-the-legs attempt.

Del Potro, the 2009 US Open champion now ranked 42nd in the world, is making his 2017 debut this week, and the rust was evident in six double-faults - five of them in the first set.

That included two in the eighth game, in which he gave back a service break.

Del Potro fought off a set point to force the tiebreaker and after securing the first set seized a 3-1 lead in the second only to again give back a service break.

A double fault on break point at four-all cost the Argentine a second break of serve and, one game later, the set.

But once he'd broken to seize a 4-2 lead in the third, Del Potro wouldn't again surrender the advantage.

On Friday, he'll face 35th-ranked Querrey, the fourth-seeded wildcard who blasted 13 aces without a double fault in dispatching fellow American Jared Donaldson 6-2, 6-3 in a second-round match at the outdoor hardcourt event.

Also reaching the final eight was 57th-ranked Belgian qualifier Steve Darcis, who ousted Georgia's Nikoloz Basilashvili 6-3, 7-5. Darcis next faces 69th-ranked American Donald Young, who rallied to defeat compatriot Taylor Fritz 4-6, 6-3, 6-4.