Six-time champions United States remained undefeated in the 2017 Hopman Cup after posting a pair of singles victories over Spain on Tuesday.

Tournament debutant Coco Vandeweghe improved to 2-0 this week as she beat Lara Arruabarrena 6-2 6-4.

Jack Sock then wrapped up the 2-0 win as he beat Spanish veteran Feliciano Lopez 3-6 6-2 6-3, to ensure the doubles match would be a dead rubber.

Vandeweghe, the Californian daughter of an Olympian mother, was dissatisfied with her serve despite earning the winning scoreline over Arruabarrena.

“I felt like my serve was all over the place, but it was good when it counted – which is important,” Vandeweghe said.

“I felt I was cruising in the second set. Hopefully I can tighten up my serve.”

Sock and Vandeweghe both won under the open roof in 39-degree Celsius conditions, typical at the height of summer in Western Australia.

Sock said that he can see room for polishing his form.

“There are things to improve for the rest of the Australian summer. I (didn’t) serve as well as I did in the first match, but I was able to dictate with my forehand from the back of the court.”