Naomi Osaka battled back from a set and a break down to defeat Anett Kontaveit 4-6 6-2 7-5 on Wednesday and advance to the Southern & Western Open semi-finals for the first time.

Former world No.1 Osaka trailed 2-0 in the second set, but she stepped up her serving and cut down on unforced errors to reel off six straight games.

The final set looked destined for a tiebreaker when Kontaveit rushed out to a 40-15 lead while serving at 5-6.

But the fourth-seeded Osaka fought back and completed the comeback when the Estonian sent a backhand wide on match point to end a contest lasting an hour and 52 minutes.

Osaka improved to 3-0 lifetime against the 12th-seeded Kontaveit.

Next up for the twice grand slam champion is a meeting with Elise Mertens, who needed just over an hour to defeat qualifier Jessica Pegula 6-1 6-3 and advance to her first Premier 5 semi-final.

The 14th-seeded Belgian frustrated Pegula throughout the match, racing around the court to extend rallies and keep pressure on the American.

Mertens, who reached the US Open quarter-finals last year, sealed the win with her third ace.

Briton Johanna Konta faces Greece’s Maria Sakkari and Belarusian Victoria Azarenka meets Ons Jabeur of Tunisia in the other quarter-finals later on Wednesday.

The tournament, the final tune-up before the US Open, is being played at Flushing Meadows in New York instead of Cincinnati due to the COVID-19 pandemic.