Williams battles past Li

Serena Williams took a firm grip on the Red Group at the WTA Championships with a 7-6 (7-2) 6-3 victory over Li Na in Istanbul.

Williams made it two wins from two in the competition so far, with both of the American's successes being achieved in straight sets.

Both players struggled to get a foothold in the match during the first set, which featured eight breaks of serve, but Williams' desire shone through in the second as she secured the win in one hour and 50 minutes.

The tone was set at the start of the match as Li dropped serve first up only to break her opponent in the next game.

Another break and two holds allowed Li to take a 4-1 lead, but Williams hit back to level before breaking again to edge ahead.

The US Open champion served for the set twice but could not convert on either occasion as her Chinese opponent hung tough to force a tie-break.

A string of errors from Li saw Williams win the breaker comfortably and then quickly break her opponent again at the start of the second set.

The scrappy nature of the contest continued, however, as Li hit straight back only for Serena to make it three breaks of serve in a row and go 3-1 up.

This time the third seed had grabbed a decisive advantage as the rest of the contest went with serve to allow Williams to complete the win.

"I started out really strong in the first game but then I started making errors and Li has been playing great to qualify for this event. She started playing her game and playing really well," Williams said of the first set.

Williams, who will play world number one Victoria Azarenka next, added: "(Azarenka) has been playing so well this year. I'm going to have to play better than I did in the first two rounds.

"But I feel like I have nothing to lose and as long as I can relax a little more I will be better."