Frances Tiafoe celebrates winning first set in Sydney on Friday.

Frances Tiafoe and Tomas Machac ahead of their United Cup match.

Petra Kvitova in action on Friday.

Petra Kvitova celebrates her victory in Sydney.

Matteo Berrettini competes for Team Italy on Friday in Brisbane.

Maria Sakkari secures victory for Team Greece in Perth. Photo Credit: Getty Images

Grigor Dimitrov supports Dimitar Kuzmanov from the Team Bulgaria player box on Friday in Perth.

Maria Sakkari and Stefanos Tsitsipas share a joke during their mixed-doubles victory on Friday afternoon in Perth.

Jason Kubler celebrates victory against Daniel Evans.

Photo Credit: TENNIS AUSTRALIA