Novak Djokovic must get to the third round of Wimbledon the hard way after falling two sets down to unseeded American Sam Querrey on Friday.

Unbeaten in 30 grand slam matches, Djokovic seemed badly affected by a lengthy delay to proceedings brought on by a combination of earlier rain interruptions and Serena Williams taking three sets to see off Christina McHale.

Querrey was red-hot, however, and benefited from the momentum gained by coming back from two sets down to beat Lukas Rosol and book his meeting with the world number one, opening up a 7-6 (8-6) 6-1 lead before more rain stunted his progress for the day.

The American made a swift statement of intent, reeling off his first three service games without allowing Djokovic to score a single point.

Djokovic saved five break points at 5-5 to scramble his way into a tie-break, where Querrey backed up his booming serve and forehand with delicate touches around the net, sealing the set in dogged fashion as the best returner in the game pushed the world number 41 all the way.

The Serbian looked far from the holder of all major titles in a woeful second set, but nothing could be taken away from Querrey after efficiently taking advantage.

A Djokovic double-fault opened the door for Querrey at 2-1 up - the world number one's ludicrously misguided hawk-eye challenge summing up his off day - and a long backhand put the American in firm control.

Querrey broke again after putting Djokovic on the spot with some defence that the Serbian would have been proud of, before sealing his two-set advantage with a booming ace, his ninth of the match.

Djokovic can perhaps take solace from his five-set win over Kevin Anderson on Court One last year, in which he also fought back from two sets down, but he will have to be vastly improved on Saturday to progress.