Zverev beats Djokovic in 2 sets to win ATP Finals title

Alexander Zverev of Germany rests on the court after winning match point against Novak Djokovic of Serbia in their ATP World Tour Finals singles final tennis match at the O2 Arena in London, Sunday Nov. 18, 2018. (AP Photo/Tim Ireland)

LONDON — Despite beating Novak Djokovic in straight sets to win the ATP Finals at only 21, Alexander Zverev knows keeping pace with the Serb isn’t going to be easy.