Ben Shelton, the young star of US tennis, has yet to lose a set on his way to the quarterfinals in Washington, reminding us that he is one of the title contenders. Frances Tiafoe, on the other hand, lost just six games as he disposed of debutant Flavio Cobolli and showed that he can keep his form at this stage of the season. This clash between two racquets who know each other very well could be the toughest test of the tournament for both of them. A three-set showdown is highly likely.