Coco Gauff defeats Naomi Osaka at the Silicon Valley Classic, Raducanu grinds out a win at Citi Open

Coco Gauff was too sharp with her return game for Naomi Osaka in the second round of the Silicon Valley Classic on Thursday, coming away with a 6-4 6-4 win.

Gauff – the world number 11 and tournament's sixth seed – created 12 break-point opportunities in the match, while only allowing one for Osaka, despite eight double-faults.

Ultimately, Gauff won 41 per cent (29-of-71) of the points off Osaka's serve, while converting 85 per cent (28-of-33) of her successful first serves into points.

Earlier in the day in a major upset, top seed Maria Sakkari was eliminated in straight sets 6-1 6-3 by American Shelby Rogers.

The world number three struggled with her serve throughout, landing only 45 per cent of her first serves, and winning just 52 per cent (12-of-23) of those points.

World number six Aryna Sabalenka needed three sets to defeat unseeded American Carolina Dolehide 5-7 6-1 7-5, and Russia's Veronika Kudermetova had less trouble dispatching Claire Liu 6-2 7-5 to set up an exciting match with Ons Jabeur in the quarter-final.

Meanwhile, in Washington at the Citi Open, Emma Raducanu played in the longest two-set match of the WTA season, defeating Camila Osorio 7-6 (7-5) 7-6 (7-4) in two hours and 49 minutes.

Both women created at least a dozen break-point opportunities, with four total breaks each as the young British star battled blisters on her hands.

Raducanu will play Liudmila Samsonova after the Russian eliminated Australia's Ajla Tomljanovich 4-6 6-3 6-2.

In the last match of the day, China's Xiyu Wang got the better of Croatia's Donna Vekic 4-6 7-5 6-1, and she will meet the winner between Tereza Martincova and Victoria Azarenka in the quarter-final.