Andrea's

The world number one prevailed 7-5 6-2 in one hour 51 minutes to go top of Group A on two wins, while Djokovic, whose performance against Nadal was hampered by an eye problem, is level with Tomas Berdych on one win after he beat Andy Roddick in the afternoon match.

Nadal broke serve in game five of the first set but Djokovic hit straight back before requiring treatment for a complaint related to his right contact lens.

The world number three looked far from comfortable as Nadal broke again for 6-5, served out the opener and then struck two decisive blows at the start of the second set to help him ease home.

"I really feel sick talking about it because it's just incredible that this happened to me. It never happened to me in my life," said Djokovic.

"I'm really annoyed something like this can really affect the match. It did because my right eye got irritated and from the 5-5 I could not play. I could not see a ball, especially on the return. It was just terrible.

"I don't want to find any excuses for my loss, but the fact of the matter is that I just could not play. I could not play. These things happen. It's out of my control. Unfortunately, it happened in a very important match, in a very important moment.

"I will try to see a doctor and see if there is something more serious going on and in two days hopefully I can be ready."

The afternoon match between Berdych and Roddick provided no shortage of entertainment, yet everyone knew the piece de resistance was still to come.