Alexander Zverev was dumped out of the Shenzhen Open at the quarter-final stage on Friday as Damir Dzumhur continued his excellent recent form with a straight-sets win.

World number four Zverev needed nearly three hours to edge out Steve Darcis on Thursday and was again short of his best as Dzumhur came from a break down in each set to triumph 6-4 7-5.

Dzumhur, who became the first player representing Bosnia-Herzegovina to win an ATP World Tour title when he triumphed in St Petersburg last week, has now won 16 of his last 19 matches.

His semi-final opponent will be Alexandr Dolgopolov, the beneficiary of Dudi Sela's retirement just one game into the third set of their encounter. The ATP attributed Sela's retirement to a forearm strain.

The other last-four tie in Shenzhen will involve second seed David Goffin, who eased past Donald Young, and Henri Laaksonen, a winner against home hope Zhizhen Zhang.

Guido Pella followed up his victory over top seed Dominic Thiem at the Chengdu Open by beating Taylor Fritz. Pella appears highly likely to face Marcos Baghdatis, who was a set and 5-2 up on Lu Yen-hsun when rain forced their match to be suspended.

Yuichi Sugita and Denis Istomin are also through to the semi-finals in Chengdu.