6-2 - A massive backhand from Serena forces the error - 15-0. Huge backhand - 30-0. But two points from the match, Li finds two stunning winners to find a chink of light at 30-30, only to lose it again when a high-kicking Williams second-serve sees Li balloon backhand. One decent first serve on the next point, and the match is over!

- - Li saves the matchpoint, concedes another after the first deuce, but Williams misses it with an over-ambitious go at a winner. Back to deuce...

5-1 - Serena cruises through another service game to find herself on the verge of the semi-finals.

3-1 - Williams holds serve with ease - and looking at her you wouldn't know for a second that she's received her biggest fright of 2009 in this match.

1-1 - Williams holds relatively easily - for the loss of just one point - and has that eye-of-the-tiger look about her now.

7-6 - Li has just not timed her shots in the tie-break: again and again she attempts dipping backhand winners, again and again she misses the lines... and then nets a straightforward forehand at 6-1 down to lose the set. You can't help but think that Williams will march on to finish this up with ease... and Li's coach obviously has the same idea, as he gives his charge a stern talking-to at the interval. We'd tell you what was being said if it weren't all in Chinese.

6-6 - Serena looks like she's going to start imposing her will on the match as she earns break point - but then Li saves the danger brilliantly with some inspired angled shots which see her opponent running everywhere. She pushes on to save the game, and we're in to a tie-break that genuinely could go either way! Could the world number one go out?

5-5 - An absolutely superb backhand winner down the line gives Li the hold to 15, and she's now within striking range of a tie-break which, on the current run of play, she would have to be favourite for. Williams has her power working well, but Li is equal to it on this evidence... and the American's shot placement is letting her down today.

- - Williams loses the plot once more, sliding to 15-40 on her own serve... Li has two break points to earn a chance to serve for the match!

4-3 - Another comfortable hold of serve for Williams as both players have started to feel the early afternoon Miami heat: the pace has definitely slowed slightly in the last few games.

3-2 - Williams holds more comfortably this time round, with the Chinese taking just one point off her opponent as her attempts at carving return winners miss the mark.

2-1 - Serena goes to advantage with a superb smash of Li's under-powered lob from the baseline, and the Chinese overhits yet another forehand on the next point to let the world number one off the hook.

1-1 - An impressive service game from Li sees her keep Serena at arm's length to race to 40-15, and though she again overhits to lose the next point while attempting a winner, she makes up for the slip with a stunning backhand down the line on the next point to wrap the game up.

4-6 - Li gets her act together following a severe talking-to from her coach at the side of the court duing the inter-game break, and picks her feet up to hold to 15 and close out the set. That's more like it - perhaps now if we can have both players performing well at the same time we'll get a decent match out here today!

3-5 - Williams continues her good work in fighting back to earn a couple of break points at 15-40 in the next game; Li fights back to deuce, but then concedes another break point and sees the game slip away as she goes wide with an attempt at a backhand winner.

1-5 - Williams shows a bit of fighting spirit at last, pushing her opponent to deuce - albeit with a bit of help from the net cord - and going to advantage straight away... And Li puts in her first double-fault!

0-4 - Williams wins the first point of the fourth game in a manner that suggests that she is about to fix things - but then loses the next four points in a row. What on earth is going on? Li is not exactly setting the world on fire, but the world number one is up to nine unforced errors already!

0-2 - Li cruises through her first service game with a string of good first serves that Serena is unable to attack effectively. It's an excellent start for the Chinese player.

- - Welcome to our LIVE coverage of Serena Williams taking on Li Na in the quarter-finals of WTA Miami. It's the third Chinese opponent in a row for Serena - and if she makes it through, she potentially faces a semi-final against her sister Venus, who players Iveta Benesova later on this evening.