Kharkiv (Ukraine): Serena Williams defeated Lesia Tsurenko 6-3, 6-2 on Sunday to send the United States back into the Fed Cup World Group by clinching a series victory over Ukraine.

The US now hold an unassailable 3-0 lead in the best-of-five playoff series after singles victories for Williams and Christina McHale on Saturday.

Williams was making her first Fed Cup appearance on foreign soil in more than a decade to help gain eligibility for the US team at the London Olympics.

"We're back in the World Group where we want to be and it feels really good to get two points," she said after the match.

Tsurenko frustrated Williams early on with accurate hitting from the baseline on the red clay court.

"What's your problem?" Williams roared at herself after hitting two consecutive aces to prevent a break in the sixth game.

The 22-year-old Ukrainian pressured Williams' serve after giving up a break, but couldn't convert two break points. Williams broke again to take the set.

"She has a good game. She has a lot of power," Williams said of her opponent.

Williams became more relaxed as the match progressed, breaking twice early in the second set.

"I had a little bit of a slow start, but I just knew that I could keep fighting," she said. "I just want to go out there and be super relaxed. I play better when I'm relaxed."

Tsurenko broke Williams to prevent her from serving out the match at 5-1, but the powerful returning of the 13-time Grand Slam champion helped her break for a third time in the set and clinch the win.

"It was hard as she was playing freely and with great confidence," Tsurenko said.

Christina McHale faces Elina Svitolina in the final singles match of the series later Sunday. Americans Liezel Huber and Sloane Stephens will play Lyudmyla Kichenok and Nadiya Kichenok in doubles.