World No. 1 Andy Murray slipped away a 4-0 lead in the decider to lose to 15th-seeded Albert Ramos-Vinolas 2-6, 6-2, 7-5 in the third round of ATP Monte-Carlo Masters on Thursday.
In their first head-to-head, Ramos-Vinolas denied Murray's hope for his first trophy of the tournament, as the top seed's best record was into the semi-finals in 2009, 2011 and 2016.
After the two players forced into a decisive third set, Murray built a comfortable 4-0 lead, while that was erased by the Spanish player to level at 4-4 with two conscutive breaks.
Murray suffered a decisive break in the 11th game, before Ramos-Vinolas grasped his second chance for the most memorable victory in his career.
"I made a few bad decisions today, which I'll look at with my team. We'll see the shots that I chose and what I would do differently," said Murray.
Coming from a month off due to a right elbow injury, Murray had to get his form back on clay for next month's French Open. He has got a wild card for next week's Barcelona Open.
Ramos-Vinolas will face No. 5 seed Marin Cilic in the quarterfinals. The Croatian eliminated ninth-seeded and 2015 runner-up Tomas Berdych 6-2, 7-6 (0).