Rafael Nadal's struggles since undergoing appendix surgery continued after marking his first competitive appearance of the 2015 season with defeat to world number 127 Michael Berrer at the Qatar Open.
Berrer lost the first set before prevailing 1-6 6-3 6-4 in the first round as the world number three suffered a second loss in as many matches since returning from going under the knife in November.
Nadal was defeated in straight sets by Andy Murray in an exhibition match at the World Tennis Championships but hopes the Spaniard could regain some match fitness with a string of outings were ended by a humbling loss to Berrer.
The 14-time grand slam champion took the first set for the loss of just one game to grab the initiative but had no answer to Berrer – who overcame three rounds of qualifying to reach the 32-man main draw in Doha – who stormed to victory.
Two break-point chances presented themselves as the qualifier Berrer served for the match in the third set but Nadal was unable to convert either of them, leaving the German to claim the biggest win of his career.
Meanwhile, world number one Novak Djokovic recovered from the illness that kept him out of the World Tennis Championship final against Murray to overcome Dusan Lajovic in straight sets to reach round two.
Ivo Karlovic, who severed his 9,000th ace during his win over Lukas Rosol, Fernando Verdasco, Dustin Brown, Richard Gasquet, Simone Bolelli and Ivan Dodig have also confirmed their place in the last 16 as preparations for the Australian Open continue.