British number one Heather Watson faces the toughest match of her life on Friday, when she meets world number one Serena Williams in the third round at Wimbledon.
Watson has never been beyond that stage of a Grand Slam. On the other hand, Williams is aiming for her 21st Grand Slam title and is on course for a so-called 'Serena Slam' of being the reigning champion all four majors - Australian Open, French Open, Wimbledon and US Open - at the same time.
But, on grass, can the girl from Guernsey defeat the best player on the planet?
Let's take a quick look at the careers so far of both players.
World number one tennis player Serena Williams has already won at Wimbledon five times and is favourite to lift the title again in 2015.
The 34-year-old has been champion at all four Grand Slam tournaments - Australian Open, French Open, Wimbledon and the US Open.
At the the 2012 London Olympics, Serena won the gold medal in both the singles and doubles tournament.
Since she turned professional in 1995, she's won 716 matches earning more than £44 million in tennis prize money.
Britain's Heather Watson was ranked 59th in the world going into Wimbledon 2015.
The 23-year-old, who was born in Guernsey, has already surprised some commentators with her win over Slovakian Daniela Hantuchová 6-4, 6-2 in the second round.
Two-time US Open Champion Tracy Austin said, ''she is really committed to her style of play and is more aggressive. It was a very impressive performance.''
She turned professional in 2010 and has won 192 matches earning more than £960,000 in tennis prize money.