Novak Djokovic's prediction that an upturn in form was just around the corner proved accurate as he kicked off his Madrid Open campaign with a straight-sets victory over Kei Nishikori.

Djokovic has struggled for consistency in 2018 due to a long-standing elbow problem but after undergoing surgery he is now pain free, and the Serbian told a news conference ahead of this week he hoped the pieces would "quickly fall into place".

And while he remains well below his previous best, there were promising signs on Monday as he battled past Nishikori 7-5 6-4.

After applying early pressure, it was Djokovic who buckled first as Nishikori's ability to keep rallies alive forced the former world number one into errors, two groundstrokes flying long to give the Japanese the break.

Nishikori was dictating proceedings as he varied his angles to keep Djokovic guessing, however parity was soon restored as the tenth seed grew in confidence.

Having let two set points slip through his fingers, Djokovic eventually took the opener with a crushing forehand off a weak second serve from his rival – the world number 12 letting out a huge roar in celebration.

Both players improved their consistency in the second set after Djokovic had to save a break point in the opening game.

Djokovic eventually turned up the heat on the Nishikori serve with the score at 5-4, upping his tempo to levels of old to fashion a match point with a deep backhand.

Nishikori's return flew long and when he repeated the feat in the next point Djokovic's job was complete, the relief evident in his face as he looks to kickstart his clay campaign ahead of the French Open.