Hello and welcome to LIVE coverage from this fourth round clash between world number one Serena Williams, five-times a former champion in Melbourne, and Ana Ivanovic, who was runner-up at Melbourne Park in 2008.

WILLIAMS 6-3 4-6 3-6 IVANOVIC - Absolutely sensational stuff from Ivanovic as she calmly goes about wrapping up the match with a service hold to love when Williams goes long with a forehand. Ivanovic is through to the quarter-finals with her very first win over Serena Williams and she awaits the winner between Casey Dellacqua and Eugenie Bouchard.

GAME, SET AND MATCH ANA IVANOVIC!!

WILLIAMS 6-4 3-6 3-5 IVANOVIC - A mis-hit backhand return from Williams across court hands Ivanovic the first point and that quickly becomes three more match points for the Serb. Good lord this is tense ...

WILLIAMS 6-4 3-6 3-5 IVANOVIC - Williams levels up at 30-all before another brilliant point from Ivanovic brings up match point. Ivanovic goes for the barn-storming forehand winner down the line only to net the ball and Williams holds with a service winner and a booming forehand. Ivanovic will serve for the match next though.

WILLIAMS 6-4 3-6 2-5 15-30 IVANOVIC - Another sensational return winner to open the game by Ivanovic before Williams levels at 15-all with a decent enough attempt at a passing shot that Ivanovic can only return wide. Ivanovic sneaks ahead again with an injection of pace on a forehand down the line that Williams pulls wide across court. And then the American is given a time violation. Could this get any more tense?

WILLIAMS 6-4 3-6 2-5 IVANOVIC - Wow! Ivanovic has not been this calm in years. She is taking it all in her stride and cruises through a love service hold of her own to leave herself potentially just one game away from a very first victory over Serena Williams. Back-to-back errors from Williams followed by a couple of huge serves from Ivanovic and the American will have to serve to stay in the match next.

WILLIAMS 6-4 3-6 2-4 IVANOVIC - Williams opens up with back-to-back aces before going on to post a second love service hold in quick succession with another couple of big serves that Ivanovic can only net in reply. Gah. This match is incredibly tense right now.

WILLIAMS 6-4 3-6 1-4 IVANOVIC - An absolutely ridiculous net-cord goes the way of Ivanovic as her backhand is going well wide until the ball catches the net and redirects in play. Ivanovic grimaces like that may have really awoken the anger in Williams, before letting herself enjoy a little grin! The Serb takes the next point with an incredible, booming forehand winner across court before going on to hold with a change of direction backhand that Williams can only net.

WILLIAMS 6-4 3-6 1-3 IVANOVIC - Williams takes an absolute age between points, way over the allowed 20 seconds, as she attempts to calm herself down and it seems to work to a point and she stops the rot and holds to get off the mark in this final set. Will one break of serve be enough for Ivanovic

WILLIAMS 6-4 3-6 0-3 IVANOVIC - Williams unleashes a huge forehand return winner to let out a spot of frustration on the opening point of the game. But Ivanovic crouches down and flicks a forehand winner down the line on her way to bringing up two game points. Williams denies her on the first with a brutal cross court forehand but a forehand return long helps Ivanovic hold and consolidate the break in this final set.

BREAK - WILLIAMS 6-4 3-6 0-2 IVANOVIC - More noise from Williams now although Ivanovic thumps a forehand return winner down the line, a forehand winner across court and a second forehand return winner down the line. It's three break points for the Serb but she only needs the one as she flicks a cross court forehand return away that Williams can only dump into the net. Extraordinary scenes on Rod Laver Arena!

WILLIAMS 6-4 3-6 0-1 IVANOVIC - Another very solid service hold from Ivanovic as she ignores all the gesturing and muttering from Williams at the other end of the net. Ivanovic belts a forehand winner down the line to seal the game as Williams shrugs towards her camp.

Absolutely brilliant stuff from Ivanovic in that second set. It's the first set Ivanovic has EVER taken from Serena in five attempts! And she is pumped!