Florida - Sixth-seeded John Isner overcame a slow start on 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 been beaten 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).
Results from the ATP Delray Beach Open on Tuesday (x denotes seeding):
1st rd
Reilly Opelka (USA) bt Ryan Harrison (USA) 7-6 (7/5), 7-6 (8/6)
Peter Gojowczyk (GER) bt Lukas Lacko (SVK) 3-6, 7-5, 6-1
John Isner (USA x6) bt Radu Albot (MDA) 5-7, 6-3, 6-4
Evgeny Donskoy (RUS) bt Darian King (BAR) 6-4, 6-2
Steve Johnson (USA) bt Nikoloz Basilashvili (GEO) 6-3, 6-4
Milos Raonic (CAN x9) bt Taro Daniel (JPN) 6-1, 7-5
Jared Donaldson (USA) bt Peter Polansky (CAN) 7-6 (8/6), 6-1
Denis Shapovalov (CAN) bt Ivo Karlovic (CRO) 7-5, 7-6 (7/4)
Franko Skugor (CRO) bt Alexander Bublik (KAZ) 6-2, 7-5
Mikahail Youzhny (RUS) bt Dudi Sela (ISR) 7-5, 6-4
Taylor Fritz (USA) bt Sam Querrey (USA x4) 2-6, 6-3, 7-6 (6/4)
Juan Martin de Potro (ARG x2) bt Jeremy Chardy (FRA) 6-2, 6-4