Novak Djokovic comes back from a set behind to see off Jenson Brooksby

Novak Djokovic survived a first set scare to defeat Jenson Brooksby (John Minchillo/AP)

Novak Djokovic survived a mighty scare before sinking wild card Jenson Brooksby in their US Open fourth round clash and staying on course for an historic calendar grand slam.

The world number one was blitzed 6-1 in an astonishing first set by the 20-year-old American, who produced just a single unforced error as he served out nervelessly to take the opener in just 29 minutes.