MELBOURNE: Second seed Novak Djokovic was forced to work hard by unwavering German Jan-Lennard Struff in his first match of the Australian Open on Monday before prevailing 7-6(5) 6-2 2-6 6-1 to stay on course for a record-extending eighth title at Melbourne Park.

Defending champion Djokovic got off to a strong start for a 5-2 lead in the opening set but the German world number 37 fought back to level things at 5-5 before going down in a closely-fought tiebreaker.

The second set proved relatively simpler for the winner of 16 Grand Slam singles titles as he converted two breakpoints while showing the same kind of form that helped him lead Serbia to the inaugural ATP Cup title before arriving in Melbourne.

Struff continued to persevere, breaking his opponent thrice in the third set, but Djokovic wrested back initiative early in the fourth to set up a second round meeting against either Japanese wildcard Tatsuma Ito or lucky loser Prajnesh Gunneswaran of India.