Nikola Mektic

Nikola Mektic, the Croatian doubles specialist, is 37 and still very much in the conversation at the top of the discipline. His ranking this season reflects steady results, with his career-high world No. 1 status a reminder of his ceiling alongside Tokyo 2020 Olympic champion partner Mate Pavic.

The numbers, though, tell a clear story. Mektic has never won a singles title, and that zero is a feature, not a bug. His game, built on sharp returns and clean net play from the right side, is wired for doubles. He remains a threat in any draw, though his current position shows a winning but unspectacular campaign relative to his peak.