Novak Djokovic: 'I will get better'

World number one Novak Djokovic has warned his US Open rivals that he is yet to reach top gear despite failing to drop a set in this year's competition so far.

The Serbian and 2011 champion eased into the fourth round by thumping Italy's Andreas Seppi 6-3 7-5 7-5 in two-and-a-half hours on Friday night.

In doing so, the 28-year-old ensured that he maintained his perfect start in Flushing Meadows, having won every set that he has played, but Djokovic says that he is not yet playing his best tennis.

"Satisfied, but you can always do better," the nine-time Grand Slam champion is quoted as saying by Reuters. "A win is a win. He is 25 in the world for a reason."

He will face Spaniard Roberto Bautista Agut in the next stage.