World number one Andy Murray blew a 4-0 lead in the deciding set as he fell to a shock defeat by Albert Ramos-Vinolas in the Monte Carlo Masters third round.
Murray went on to lose 2-6 6-2 7-5 in only his second match back after a month out with an elbow injury.
Two breaks had the Briton in command of the third set, but Spanish 15th seed Ramos-Vinolas hit back with successive breaks to set up a famous victory.
Marin Cilic awaits Ramos-Vinolas in the last eight after beating Tomas Berdych.
Murray, 29, was playing his first tournament since being beaten in the second round at Indian Wells in March.
He beat Gilles Muller in straight sets on Wednesday, but admitted afterwards his elbow injury was still causing him some problems.
Murray began his second-round match against Muller with three double faults in the first four points of the match, and his service game was again an issue against Ramos-Vinolas.
The Scot was broken seven times as 29-year-old Ramos-Vinolas claimed a first ever win against a world number one.
Murray showed trademark fight in fending off three break points at 4-4 in the decider, but could not respond when the Spaniard was in the ascendancy in his next service game.
Murray briefly threatened to break back with the score at 30-30 as Ramos-Vinolas served for the match, but he dragged a forehand wide and misjudged a drop shot into the net at match point.
Jamie Murray, meanwhile, made a winning start, joining forces with Bruno Soares to beat Tommy Haas and Treat Huey 6-3, 6-2 in the last 16 of the men's doubles.