File Photo: Ons Jabeur hits a return to Ajla Tomljanovic during their U.S. Open women s singles quarterfinal in New York. AFP
In another surprise, Canadian Bianca Andreescu, the former U.S. Open winner now ranked 31st, overcame seventh seed Maria Sakkari of Greece 5-7, 6-3, 6-4, in a gruelling three-hour, three-minute battle in the early afternoon South Florida sun.
Tunisian Jabeur, beaten finalist at Wimbledon and the US Open last year, has been working her way back from injury and on her return earlier this month went out in the third round at Indian Wells.
Jabeur underwent surgery after suffering a knee injury at the Australian Open, and subsequently missed the WTA Tour's Middle East swing.
She looked well short of her best against the 22-year-old Gracheva and had two medical visits during the one-hour 11-minute match.
The win was the biggest scalp yet for Gracheva, who earlier this month reached her first WTA final, losing in Austin to Ukraine's Marta Kostyuk.
"The plan was, of course like all matches, to be as stable as possible, to try to make her work as much points as possible, and of course wait for comfortable ones to attack," Gracheva said after her third career win over a top ten opponent.
"I've just probably caught this wave where I'm stable, where I always have a chance to play my game, be aggressive, cause troubles for the others by the game style. I've just got to try to keep rolling on this way," she added.
Andreescu, the US Open winner in 2019, had eliminated Britain's Emma Raducanu in the previous round and after losing the first set to Sakkari's powerful stroke play, the Canadian settled into a solid pattern of steady returns, peppered with aggressive winners as she took control of the second set.
She took advantage of some loose play from Sakkari but was unable to convert on two match-points at the end, offering a glimmer of hope to her opponent, but finally grabbed the win when the Greek found the net.
Andreescu has now claimed three wins over top ten opponents since returning to the tour last April from a six-month mental-health related hiatus.
Karolina Pliskova of the Czech Republic advanced with a 6-2, 6-4 win over China's Wang Xinyu and her compatriot Barbora Krejcikova also enjoyed a straight sets win, 6-3, 6-2 against Belarusian Aliaksandra Sasnovic.
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