Juan Martin del Potro overcame Damir Dzumhur to reach the quarter-finals of the Delray Beach Open as Sam Querrey kept his title defence alive.

Del Potro continued his comeback with a 7-6 (7-5) 4-6 6-3 victory over Dzumhur on Thursday.

Featuring in just his second match of the ATP Tour season, 2009 US Open champion and seventh seed Del Potro - hampered by ongoing wrist problems - converted three of 12 break point opportunities to book his spot in the last eight.

After almost two and a half hours on court, Del Potro will next face defending champion Querrey.

American fourth seed Querrey eased past countryman Jared Donaldson 6-2 6-3 at the ATP 250 event.

Querrey - who defeated Del Potro in the semi-finals of last year's tournament - sent down 13 aces and did not drop serve throughout the contest.

Donald Young progressed to the semis following the withdrawal of Steve Darcis.

Darcis was due to face Young in the quarter-finals after defeating Nikoloz Basilashvili 6-3 7-5 earlier on Thursday but the Belgian was forced to withdraw.

Young had outlasted Taylor Fritz 4-6 6-3 6-4 in the round of 16.