John Isner beats Radu Albot to reach second round at Delray Beach

DELRAY BEACH, Fla. -- Sixth-seeded John Isner overcame a slow start Tuesday to win his rematch against Radu Albot in the first round of the Delray Beach Open, 5-7, 6-3, 6-4.

Isner lost to Albot last week in the first round of the New York Open, and had lost in the opening match of his three previous tournaments this year.

No. 2 Juan Martin del Potro broke serve four times to beat Jeremy Chardy 6-2, 6-4. No. 9 Milos Raonic, last year's runner-up to champion Jack Sock, swept the final five games and beat Taro Daniel 6-1, 7-5.

Ivo Karlovic, the 2015 champion, converted only one of 12 break-point chances and lost to Denis Shapovalov 7-5, 7-6 (4).