World No 1 Andy Murray lost 6-3, 6-3 to unseeded Borna Coric in the Madrid Open third round on Thursday as his difficult start to the claycourt season continued, while Rafa Nadal and Novak Djokovic eased into the quarter-finals.
The Briton played poorly in the first set, losing three service games and looking increasingly frustrated.
Murray was on the verge of being broken in his first service game in the second set before recovering and then earned two break points in the third game but was unable to take advantage.
He surrendered his serve in the seventh game, giving the 20-year-old Coric three break points.
World No. 59 Coric took the second break point to serve out for the match, sending last year's finalist and two-time Madrid champion Murray packing.
Murray also lost at the last-16 stage in last month's Monte Carlo Masters, his first tournament after recovering from an elbow injury, and was then beaten by Dominic Thiem in the Barcelona Open semi-finals.
"Most things weren't working particularly well. I started the match okay, but when I started to go behind, I didn't find any way to improve my game or to make it more difficult for him," Murray told a news conference.
"I didn't help myself find a way into the match to start playing better. That was disappointing because you're not always going to play your best tennis but you can still find ways to make it difficult for your opponent and I didn't do that today.
World number two Djokovic also reached the last eight with a 6-4, 7-5 over Feliciano Lopez, while crowd favourite Nadal made light work of the lacklustre Nick Kyrgios, winning 6-3, 6-1.
Defending champion Djokovic had fewer problems against the 35-year-old Spaniard than in his three-set second-round test with Nicolas Almagro on Wednesday, taking the first set 6-4 before breaking in the 12th game of the second to avoid a tie-break.
Rain in the Spanish capital meant the roof on the Manolo Santana court was closed for the game, slowing down Lopez's powerful serve to the advantage of the Serb, who recently split from his long-term coach Marian Vajda.
Four-time champion Nadal, the only Spaniard left in the tournament, demolished Kyrgios, who lost interest as the match progressed, provoking boos from the crowd.
Nadal meets David Goffin in the quarter-finals on Friday after the Belgian beat Milos Raonic 6-4, 6-2, while Djokovic will play Japanese sixth seed Kei Nishikori, who saw off David Ferrer of Spain 6-4, 6-3.
German Alexander Zverev also reached the last eight by beating Czech Tomas Berdych and will play Pablo Cuevas of Uruguay, while Coric will play Dominic Thiem, who lost the Barcelona Open final to Nadal last month.