Madison Keys
One could perhaps argue world No. 9 Madison Keys is already at the top, and that would not be an incorrect assumption. But at only 22, Keys is playing some of the best tennis on tour. The two-time WTA title winner appears to be following a career path fairly similar to that of her idol, Serena Williams, and is already most comfortable on grass courts.
Keys is also the first American woman to be ranked inside the top 10 since Serena Williams, who achieved the feat in 1999, and has also had success at Grand Slams, making the semi-finals of the Australian Open in 2015.
Incidentally, Keys lost to Serena Williams at the finals of the WTA Premier event in Rome last year, played on clay, following it up with her title at the Aegon Classic on grass – proving her comfort on all surfaces.
As a result of that performance, Keys made the WTA Finals last year, although her run there ended in the group stages; this year, she is drawn against the powerful Naomi Osaka in the Round of 32 at Indian Wells.
Considering she is already a consistent top 10 player, it is not a far stretch to think that the American grass court specialist could well be a future World No. 1!