Ukrainian Elina Svitolina knows first hand the dangers of relaxing in tennis - especially when you're in a winning position against world No.1 Serena Williams.
Svitolina is a star in the making after shooting up to 19th in the world in 2015.
The 21-year-old has set her sights on crashing into the world's top 10 this year, and her bid will receive an early test when she takes on Williams at the Hopman Cup on Monday.
Svitolina hasn't beaten Williams in their three previous encounters.
But she came close in last year's Australian Open, when she won the first set 6-4 before being walloped in the following two sets.
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Svitolina said facing Williams was a multi-pronged challenge.
"Sometimes she starts slowly," Svitolina said.
"She goes into the match not ... ready 100 per cent, but then she plays really well as the match goes on.
"It makes it really tough because you never know if she's going to serve an ace, or a double fault, or it's going to be a normal point.
"She has a huge serve and it always works for her in important moments. That's why she is such a great champion.
"I'm just taking this match as a great opportunity to improve my game and to get experience to play against her."
Svitolina will team with Alexandr Dolgopolov to represent Ukraine at the January 3-9 Hopman Cup at Perth Arena.
The right-hander is desperate to continue her rise up the ranks this year.
But to do that, she knows she needs to drastically improve her grand slam results.
In 10 grand slam appearances, Svitolina's best result has been a quarter-final appearance at the 2015 French Open.
Her next best were third-round appearances at the US Open (2015) and Australian Open (2015, 2014).
