Feeling more doubts than in his previous appearance at the ATP clay court event, but showing more determination in the important moments, the two-time Madrid Open champion prevailed over the 2014 runner-up in one hour and 59 minutes, reports Efe.
Earlier this year, Djokovic underwent surgery for a right elbow injury, which has marred his last few seasons.
The Manolo Santana center court saw ups and downs for Djokovic, who was overwhelmed by Nishikori's speed in the long rallies and committed some odd unforced errors.
Djokovic remained cool-headed, however, putting pressure on his rival when it mattered and converting three out of seven break points he created.
For a place in the last-16, Djokovic is to play either Kyle Edmund of United Kingdom or Germany's Alexander Zverev.
Djokovic, a former world No. 1, seeks to return to top form ahead of the French Open, something he failed to achieve at the Monte Carlo Masters last month when he was knocked out by Dominic Thiem in the third round.
The 12-time Grand Slam champion, who rehired Slovakian coach Marian Vajda and lightened his racquet to prevent a right elbow setback, had asked for a wild card to take part in the Barcelona Open last month, but lost in his first match to Slovakia's Martin Klizan.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
