BELGRADE, Serbia — Defending champion Novak Djokovic advanced to the quarterfinals of his hometown tournament Thursday by beating Fabio Fognini of Italy 6-4, 6-4 in the second round of the Serbia Open.

Djokovic broke three times in each set in a match where both players struggled with their serve.

John Isner of the United States made it to his first quarterfinal since February by defeating Josselin Ouanna of France 6-2, 6-4 , while Richard Gasquet ousted Andreas Seppi of Italy 4-6, 6-2, 7-5.

Serbian teen wild-card Filip Krajinovic rallied to beat Horacio Zeballos of Argentina 6-3, 1-6, 7-6 (5) for his first ATP Tour quarterfinal.

The Serbia Open is organized by the Djokovic family.