Madison Keys among those into third round at Flushing Meadows

It was a great start to another steamy day for the Americans with 19th seed Keys needing just 54 minutes on centre court to race past Czech Tereza Smitkova 6-1 6-2 and reach the third round for the first time four tries.

The victory marked another milestone in what has been Keys's best grand slam season having reached the Australian Open semi-finals, Wimbledon quarters and third round of the French Open.

"So far this year it's probably been the best year I have had," said Keys. "It hasn't been perfect. There have been some ups and downs but I think that's the nature of tennis.

"I still haven't quite figured everything out."

Kristina Mladenovic (France) beat Bojana Jovanovski (Serbia) 7-5 6-1

Bethanie Mattek-Sands (U.S.) beat CoCo Vandeweghe (U.S.) 6-2 6-1

15-Agnieszka Radwanska (Poland) beat Magda Linette (Poland) 6-3 6-2

Roberta Vinci (Italy) beat Denisa Allertova (Czech Republic) 2-6 6-3 6-1

Anett Kontaveit (Estonia) beat 31-Anastasia Pavlyuchenkova (Russia) 7-5 6-4

Darya Kasatkina (Russia) beat Ana Konjuh (Croatia) 6-4 6-4

19-Madison Keys (U.S.) beat Tereza Smitkova (Czech Republic) 6-1 6-2

Madison Brengle (U.S.) beat Anna Tatishvili (U.S.) 6-3 6-2