MELBOURNE, Jan 26 (Reuters) - On ‌tennis's biggest stages, Alexander Zverev plays by the arena's timing, the serve clock and ‌the changeover, while a quieter countdown of his blood sugar runs beneath the noise.

"There ‌are definitely two games happening at the same time: there's the match everyone sees and then there's the one only I feel," Zverev told Reuters recently, describing life with type 1 diabetes.