How far can Venus Williams go in this tournament? How do you think she would fair against sister Serena should they both make the semi-finals? Who is your tip to claim the women's title? Answers in the form of a tweet (#bbctennis) or text (81111 - UK only) would be good...

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Victory for Venus today will mean she remains on course to meet sister Serena in the semi-finals after the latter came through a nervy fourth-round match against Garbine Muguruza 2-6 6-3 6-2.

It was anything but vintage from the American top seed, who suffered a mid-game coughing fit on her way to grinding out victory on Rod Laver Arena.

"I think I caught that bug," said the American. "I've just been sick. I've been fighting it with vitamin C and all kinds of stuff. But I just have a really bad cough."

Venus Williams has never won the Australian Open - her best showing came in 2003 when she was beaten by sister Serena in three sets. And at 34, the odds of her doing so now are not in her favour. But that won't stop the American trying.

"I do my best every single day," said the seven-time major champion. "That's pretty much the way it goes. I think just not being afraid is the most important thing."

"I like to win titles, whether it's a smaller event or a big event. That's what I play for. So, yes, it's great to be in the second week. But is the fourth round my goal when I come to these tournaments? No."

Image source, Getty Images

Morning everybody and a very warm welcome to our live coverage of an absolute cracker of a fourth-round tie at the Australian Open, the year's first Grand Slam.

American Venus Williams, in the twilight of her tremendous career at 34, takes on sixth seed Agnieszka Radwanska, a former Wimbledon finalist.

The winner will take on American Madison Keys, who beat fourth seed Petra Kvitova earlier this week, in the quarter-finals.

Image source, EPA

Reaching the fourth round of a Grand Slam used to be a given for Venus Williams. Winning majors with that familiar smile was more her forte.

But things changed when she was diagnosed with Sjogren's Syndrome - an autoimmune disorder that has left her lacking energy at tournaments, in 2011.

Winner of seven Grand Slams, her last triumph came back in 2007. Her last fourth round appearance was nearly four years ago at Wimbledon.

But at Melbourne Park this year, the American has looked stronger and quicker than she has done for years while that gritty, dogged determination remains.

The smile is back. Venus is back. The question is: how far can she go?