The top seeds were all victorious in Thursday's action at the Atlanta Open, with John Isner prevailing 7-6 (10-8) 4-6 7-6 (7-3) in an all-American showdown against Ben Shelton to close the day's play.

Isner, 37, relied as he usually does on his trusty serve to get the job done in tiebreakers, winning the match despite not breaking Shelton's serve a single time.

The second seed won 85 per cent (60-of-71) of his successful first serves, while Shelton was similarly stout, converting 83 per cent (50-of-60).

Isner will meet fellow American Jenson Brooksby in the quarter-finals after he came back from an early break to defeat Mackenzie McDonald 6-3 6-4.

The biggest differentiating factor between the two players was Brooksby's effectiveness off his second serve, winning 61 per cent (14-of-23) of those opportunities compared to just 22 per cent (four-of-18) from McDonald.

Fourth seed Alex de Minaur defeated fellow Australian James Duckworth 6-4 6-4 in a competitive match, but De Minaur simply created more chances for himself, with five break point opportunities while Duckworth had two.

De Minaur will play France's Adrian Mannarino after he defeated American Andres Martin 7-5 6-3.

Mannarino's main advantage was with his return game, securing four breaks of serve while dropping his own serve only once.