BELGRADE, Serbia (AP)—Top-seeded and defending champion Novak Djokovic retired with breathing problems during his quarterfinal match against Filip Krajinovic at the Serbian Open on Friday.

That’s why the moment it ended, Djokovic let out a belated roar towards his court-side box, where Andy Murray paused for a ...

Djokovic, who experienced breathing and stamina problems when he first came on tour, switched to a gluten-free diet and rose to No. 1 in the world in 2011. He credited his new endurance to the ...

Murray has regularly cut a tense figure during Djokovic's run at Melbourne Park, appearing deep in thought about ... showed with a heavy exhale of breath. Then came the moment when Djokovic ...