The big-serving Croatian, the fifth seed, lost 6-4 6-4 in the opening match on centre court -- a result all the more surprising as it was only the diminutive Schwartzman's third career victory on grass.
Cilic, who beat Novak Djokovic to win the title for the second time last year, never looked entirely comfortable and dropped serve three times as he slipped to defeat.
Second seed Kevin Anderson, runner-up at Wimbledon last year, also suffered a surprise second-round defeat as he was beaten 6-1 4-6 6-4 by Frenchman Gilles Simon.
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Greek top seed Stefanos Tsitsipas, making his debut at the prestigious Wimbledon warmup event, belatedly moved through to the second round as he finished off home hope Kyle Edmund 6-3 7-5 having come off the previous night at 3-3 in the second set.

Stefanos Tsitsipas of Greece celebrates victory after his First Round Singles Match against Kyle Edmund of Great Britain during day Four of the Fever-Tree Championships at Queens Club on June 20, 2019 in London, United Kingdom.

Image credit: Getty Images

Tsitsipas needed seven match points to end home interest in the singles draw and set up a clash, later on Thursday, with Frenchman Jeremy Chardy. Organisers have a packed schedule to get through on Thursday after Tuesday was washed out and only a handful of matches were completed on Wednesday. Three first-round matches were still to be completed at the start of play on Thursday. (Reporting by Martyn Herman Editing by Toby Davis)
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