Daniil Medvedev has gone underarm in his defeat of Alexander Zverev on day two of the ATP Finals

Medvedev used an underarm serve as he prevailed 6-3 6-4 over the 2018 champion, while Novak Djokovic cruised past tournament debutant Diego Schwartzman 6-3 6-2 in an empty O2 Arena in London.

Medvedev led 4-3, 30-30 in the second set when he surprised Zverev with a quick underhand serve.