Coco Gauff sealed her place in the WTA Finals semi-finals thanks to a shock win over long-term rival Iga Swiatek on Tuesday.
Third seed Gauff beat reigning WTA Finals champion Swiatek 6-3, 6-4 in the second round of group stage action, just a second win for the American in 13 tour meetings against the Pole.
Gauff was in cruise control in the first set, breaking twice, and then twice came from a break down to close out the match in straight sets – overcoming a spate of double faults.
Victory means the world No 3 is assured of her place in the semi-finals, no matter what happens in her final group stage match against Barbora Krejcikova on Thursday.
"It feels great – I knew going into it despite our head to head I had a lot of confidence," said the American.
"I felt like I was playing great tennis. Even when I was playing a bit sloppy, the games I lost were still going to deuce. They gave me confidence, I knew if I could stay solid, I'd have the chance to close out the match.
"The first set I had like three straight games in a row with break points. I didn't let it discourage me – I knew I'd get it eventually.
"Even in the last game I missed two forehand returns in the net and I told myself: 'it's ok I'll get the next one', and I did."
Aged just 20 and already a former world No 2 and US Open champion, Gauff has hit plenty of 'youngest' player milestones across her career.
She has now reached back-to-back semi-finals at the year-end championships, having also made the last four in Cancun 12 months ago.
That makes her the youngest American woman to reach consecutive semi-finals at the WTA Finals since Tracy Austin in 1979 and 1980.
Gauff will hope to emulate her compatriot and former world No 1 by going on to lift the title, which Austin was able to do in 1980 – downing Martina Navratilova in the final.
In her third WTA Finals appearance, the 20-year-old has now won both her first two group stage matches for the first time.
That makes her the first player in 17 years to achieve that before turning 21, emulating Maria Sharapova and Ana Ivanovic's feat from the 2007 Finals.
Both former world No 1's went on to make the last four, much like Gauff, with Ivanovic falling in the last four and Sharapova beaten in the final; both women were defeated by Justine Henin.
