PERTH - THE United States made it two wins out of two at the Hopman Cup on Monday when Tomas Berdych retired through illness midway through the mixed doubles of their encounter with the Czech Republic.

World number seven Serena Williams had put the United States ahead with a hard-fought 6-0 2-6 7-5 victory over Lucie Safarova.

Berdych was a doubtful starter because of a virus and organisers had allowed him to play the mixed doubles first in the hope that it would help him complete the match.

Looking fitter than in recent years, Williams, who only arrived in Perth on Sunday because of a recent stomach virus, began superbly against Safarova, racing through the first set in just 22 minutes.

Safarova was also struggling to overcome a similar illness to that of her boyfriend, Berdych, but she improved as the match wore on, surging to a 3-0 lead and then holding on to level the match.

Hitting a series of winners, particularly down the line, it looked like world number 23 Safarova would cause an upset when she led 4-2 in the third set and held a point for a 5-2 lead.

But Williams hit back and after levelling at 4-4, she broke again in the 11th game before serving out for victory.

'I know Lucie's a great player so I knew it was going to be a tough match,' Williams said.

'After the first set, I thought, 'I'm on my way to victory' and the next thing I know, I'm almost down 5-2 in the third.' With Meghann Shaughnessy standing in for the late-arriving Williams, the United States beat India 2-1 in the opening match. They play Australia in their final Group B match on Thursday.

The winners of both groups at the eight-nation mixed team event will meet in Friday's final. -- REUTERS