Djokovic missed the second half of 2017 with an elbow injury that required surgery and only just made it back in time for the Australian Open.

The Serb admitted he was still not sure how the problem would hold up as the tournament started and has been sporting a supporting sleeve on his right arm.

The 30-year-old has also changed his serving action in an effort to take some pressure off the joint - but it was not his elbow that appeared to be troubling him.

Having taken the first set 6-2 in 41 minutes and looking relatively comfortably, Djokovic called for the trainer and took a lengthy medical timeout.

The former world No 1 appeared to be having treatment for a lower back issue, although he seemed to be having trouble all down his left side, but refused an apparent offer of painkillers on court.

But he chose to continue on in the match and upped his aggression in an effort to shorten the points and minimise the stress on his back.

Djokovic continued to feel his left side, walking with a slight limp and hopping pain after playing certain shots.

However, the added aggression appeared to work against Ramos-Vinolas and the world No 22 in the very next game to leave him a massive underdog, even against a hampered Djokovic.

He went on to seal the second set 6-3 and take a commanding lead in the match.