- Electronic line calls come into question again as Alexander Zverev takes photo of ball mark Flashscore.com
- Alex Zverev given warning after using phone to take photo of disputed ball mark in Madrid Open victory CNN
- Alexander Zverev wins amid controversy in Madrid Tennis.com
- Zverev survives Davidovich Fokina scare in Madrid ATP Tour
- Alexander Zverev adds to clay line-calling furore during Madrid Open win The New York Times