FACTBOX-Tennis-Simona Halep v Serena Williams

A look at the records of Romanian Simona Halep and American Serena Williams before their fourth-round match at the Australian Open on Monday (prefix number denotes seeding): 1-SIMONA HALEP

Age: 27 WTA Ranking: 1

Grand Slam titles: 1 (French Open 2018) 2018 Australian Open performance: Runner-up (2018)

Best Australian Open performance: Runner-up (2018) Halep can cover the court quickly despite her 1.68-metre frame and she has the ability to surprise opponents with winners even when she is on the back foot.

The Romanian was stretched to three sets in victories over Kaia Kanepi and Sofia Kenin but she was back to her ruthless best to knock out Venus Williams in the third round. 16-SERENA WILLIAMS

Age: 37 WTA ranking: 16

Grand Slam titles: 23 (Australian Open 2003, 2005, 2007, 2009, 2010, 2015, 2017; French Open 2002, 2013, 2015; Wimbledon 2002, 2003, 2009, 2010, 2012, 2015, 2016; U.S. Open 1999, 2002, 2008, 2012, 2013, 2014) 2018 Australian Open performance: Did not play

Best Australian Open performance: Winner (2003, 2005, 2007, 2009, 2010, 2015, 2017) An intimidating opponent at the best of times, the 23-times Grand Slam champion can win battles even before they begin.

The American has managed to conserve energy with three convincing wins against Tatjana Maria, Eugenie Bouchard and Dayana Yastremska -- spending just over three hours on court in total. HEAD-TO-HEAD (Halep 1 - Williams 8)

2016 Williams d Halep 6-2 4-6 6-3 (U.S. Open, hard) 2016 Williams d Halep 6-4 6-3 (Indian Wells, hard)

2015 Williams d Halep 6-3 7-6(5) (Cincinnati, hard) 2015 Williams d Halep 6-2 4-6 7-5 (Miami, hard)

2014 Williams d Halep 6-3 6-0 (WTA Finals Singapore, hard) 2014 Halep d Williams 6-0 6-2 (WTA Finals Singapore, hard)

2013 Williams d Halep 6-0 6-4 (Cincinnati, hard) 2013 Williams d Halep 6-3 6-0 (Rome, clay)

2011 Williams d Halep 3-6 6-2 6-1 (Wimbledon, grass) (Reporting by Hardik Vyas in Bengaluru; Editing by Clare Fallon)