World number one Simona Halep swatted aside American Nicole Gibbs while Maria Sharapova was flawless in her straight sets victory over Romania's Mihaela Buzarnescu in the opening round of the Shenzhen Open on Monday.
Roger Federer suffered a shock 3-6, 6-3, 7-6(4) defeat to Australian wildcard Thanasi Kokkinakis on Saturday that will cost the Swiss his world number one ranking and leaves the Miami men's tournament wide open.
It was the Russian's first competitive match since she withdrew from the St Petersburg Open in January.
The seventh-seeded Bulgarian advanced to his eighth ATP World Tour Masters 1000 quarter-final with a 6-3, 7-5 victory over Del Potro, who struggled with the intense heat in the closing stages of the one hour, 39 minute match.
Cilic marches past Querrey into Queen's semis
Roger Federer rallied from a set down to beat Moldovan surprise package Radu Albot 4-6, 7-5, 6-3 in a stuttering start to the 20-times Grand Slam champion's Miami Open campaign on Saturday.
IMAGES from the Australian Open on Tuesday.
Ukrainian fourth seed Elina Svitolina powered into the third round of the U.S. Open with a 6-4, 6-4 win against Russian Evgeniya Rodina on Thursday.