BEIJING (AFP) - Former US Open champion Marin Cilic dropped a set against Australia's John Millman before reaching the Shenzhen Open quarter-finals on Thursday.

The Croatian second seed, still without a title this year, was troubled by the 75th-ranked Millman before winning 6-3, 4-6, 6-3, helped by six aces in the final set.

"I was generally happy with my performance in the first set," Cilic said, according to the ATP website. "In the first game of the second set, he hit good returns. Then he served really well after that.

"It was not easy to get back in the match. The conditions are really humid, so you have to be prepared. It's more demanding physically, but I served well and that helped me get some free points at critical moments." Cilic, 27, will next face Hyeon Chung after the South Korean's 6-2, 6-0 victory over Britain's Aljaz Bedene.

Elsewhere Adrian Mannarino of France beat China's Yan Bai 7-5, 7-6 (9/7) to set up a quarter-final against Spaniard Guillermo Garcia-Lopez, who downed Lukas Rosol 6-4, 6-3.