The 14,061-seat stadium became the second arena at the Billie Jean King National Tennis Centre to boast a retractable roof after a $600million (£465m) rennovation - and it may well boast the biggest upset of the 2018 event already as Halep was blown away on the first day of the final Grand Slam of the year.
Kaia Kanepi of Estonia, right, greets number one seeded Simona Halep of Romania after their 2018 US Open women's match August 27, 2018 in NY. World number one retrieved a double break in the second set to get back to 4-4 but the Romanian got broken again and the Estonian held to serve out the match. Kanepi has shown the occasional ability to grab significant results, including a run to the quarterfinals at Flushing Meadows a year ago - when Halep also lost in the first round.
She lost 6-2, 6-4 in just 75 minutes to world No. 44 Kaia Kanepi, of Estonia.
Frustration for Halep boiled over in the second game of the second set when she smashed her racket on the court, earning a racket abuse warning from the chair umpire.
Eventually, Halep got going a bit, taking advantage of Kanepi's mistakes to break back twice and get to 4-all in that set, getting a lot of support from fans who repeatedly chanted her first name.More news: Nazanin Zaghari-Ratcliffe reunited with daughter after temporary Iran jail release
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Kanepi advances instead, moving on to play qualifier Jil Teichmann in the second round. Kanepi, who came within two points of victory before losing their lone encounter at 2014 Doha, was asked what was the secret to her win over Halep, BBC reported.
Halep won the French Open in June for her first Grand Slam title and is assured of remaining at No. 1 after the US Open, even with her first-round departure.
"I was thinking about that: Why (did) they cheer so much for her?" Last year, the U.S. Open began with eighth players vying for the No. 1 ranking.
Simona Halep won in Montreal this summer, and looked superb while doing it.