Zverev was already heated earlier in that game, when a spectator yelled “out” during a point. Zverev complained about it to Forcadell, who asked the crowd not to shout during points. After losing the next point, Zverev was warned about showing too much frustration.

Alexander Zverev was left bemused after the umpire stopped play in the middle of a rally when a bird's feather floated down on the court during his quarter-final against Tommy Paul at the Australian Open on Tuesday.

Watch Alexander Zverev argue with the umpire after he halts play mid-rally because of a feather on court during the German's Australian Open quarter-final victory over Tommy Paul.