Djokovic, winner of two of the last three editions in the Principality and the player who has dominated the ATP rankings over the past two seasons, was unable to mount a recovery against an opponent who got the upper hand by winning the opening set.

Djokovic came to the court with 22 consecutive wins in Masters 1000 play, with his last defeat coming in August in Cincinnati against Roger Federer.

The world number one had won his last 14 matches and holds four titles already in 2016, including the US Masters double from last month in Indian Wells and Miami.