Novak Djokovic continued his pursuit of a calendar Grand Slam by reaching the US Open third round with a straight-set win over Dutch rival Tallon Griekspoor.

Djokovic, aiming to become only the sixth player to complete a clean sweep of the Australian Open, French Open, Wimbledon and US Open, won 6-2 6-3 6-2.

It was a solid display but the top seed was ruffled by a heckler at one point.

Alexander Zverev, among those expected to challenge the Serb, advanced with a rapid win over Albert Ramos-Vinolas.

In the quickest completed men's singles match so far, 24-year-old fourth seed Zverev needed just one hour and 14 minutes to win 6-1 6-0 6-3 against the Spaniard and reach the third round.

While Djokovic could not match that speed, it was a similarly-dominant performance from the 20-time Grand Slam champion against 121st-ranked Griekspoor.