PERTH, Australia (AP) CoCo Vandeweghe gave the United States an early lead and Jack Sock clinched the Americans' opening match Sunday at the Hopman Cup mixed teams tournament.
Vandeweghe beat Lucie Hradecka 6-4, 6-2 before Sock defeated Adam Pavlasek 7-5, 3-6, 6-3 to clinch the match against Czech Republic.
The two Americans also beat Pavlasek and Hradecka 2-4, 4-2, 4-1 in the mixed doubles, which this year features the Fast4 format, including a tiebreaker at 3-3 in each set and no advantage on points.
Hradecka replaced two-time Wimbledon champion Petra Kvitova after Kvitova was injured 10 days ago in a knife attack by an intruder in her home in the town of Prostejov. Kvitova is expected to be off the tour for up to six months.
''I played a decently clean match, it's always going to be a little bit interesting your first time out on the court,'' Vandeweghe said. ''A little pre-match jitters but I thought I did a good job.''
The United States has won the Hopman Cup a record six times in the tournament's 28-year history.
Defending champions Australia, represented by Russian-born Daria Gavrilova and Nick Kyrgios, lost the late match Sunday against Spain. Kyrgios beat Feliciano Lopez 6-3, 6-4 in the opener before Spain's Lara Arruabarrena defeated Gavrilova 7-5, 6-1. Spain won the mixed doubles 4-0, 4-2 involving the same players.
Roger Federer, making his return after a six-month left knee injury layoff, and Belinda Bencic begin play for Switzerland against Britain, represented by Heather Wilson and Dan Evans, on Monday night.