Roberto Bautista Agut knocked out by Chung Hyeon

The Spanish world number 13 and tournament's ninth seed, who was beaten in last year's final by Andy Murray, lost 6-4 6-3 in straight sets against the 21-year-old from South Korea, who broke Bautista Agut in his final two service games to secure victory.

World number 38 Benoit Paire is also out after the Frenchman lost 6-4 6-4 to 19-year-old American Frances Tiafo and Greek qualifier Stefanos Tsitsipas beat Russian Karen Khachanov 7-5 6-3.

Juan Martin Del Potro, though, avoided an upset when the 16th seed from Argentina came through in three sets, 6-2 3-6 6-4, against Nikoloz Basilashvili of Georgia.

British number two Kyle Edmund defeated Jiri Vesely 6-3 6-2 to set up a second-round match against fourth seed Marin Cilic.

Spain's Feliciano Lopez, the world number 34, beat big-serving Croatian Ivo Karlovic 7-6 (7/1) 7-6 (8/6) while compatriot Albert Ramos-Vinolas came from behind to see off Portuegse Joao Sousa 3-6 6-3 7-5.

Richard Gasquet will play Chung after the Frenchman recovered from losing the opening set tiebreak to beat Dutchman Robin Haase 6-7 (11/13) 7-5 6-2.

Monday's late matches saw Andrey Rublev of Russia come through in three sets 6-1 4-6 6-1 against Bosnian Damir Dzumhur, while Chinese player Di Wu knocked out Frenchman Jeremy Chardy, beating the world number 83 in straight sets, 7-6 (7/2) 6-2.