Bulgaria's Grigor Dimitrov outplayed Andy Murray on Centre Court to end the Briton's Wimbledon title defence.
Dimitrov, 23, played superbly to win 6-1 7-6 (7-4) 6-2 in two hours and one minute and reach his first Grand Slam semi-final.
Murray had been on a 17-match winning streak at Wimbledon and was looking to reach his sixth consecutive semi-final.
However, Dimitrov's big serve, variety of shots and athletic defence proved too much for Murray.
The atmosphere on Centre Court was in marked contrast to 12 months ago, when 15,000 thrilled spectators watched Murray become the first Briton since Fred Perry in 1936 to win the men's singles.
In the year that followed, Murray had back surgery in September and lost the services of coach Ivan Lendl in March, with Frenchwoman Amelie Mauresmo stepping into the role on the eve of Wimbledon.
But only four men in the open era - Bjorn Borg, Boris Becker, Pete Sampras and Roger Federer - had returned after their first Wimbledon victory to defend the title, and despite impressing in the earlier rounds, Murray fell well short against 11th seed Dimitrov.
"My start to the match was poor," said Murray. "I started the match badly and I think that gave him confidence.
"I should have done a better job at the beginning of the match of making it tougher for him, and I didn't manage to do that.
"Also, when I got back into the second set, that was my opportunity there."
The 27-year-old Scot, whose winning run at SW19 included his 2012 Olympic gold and last year's Wimbledon triumph, could not convert a break point in a tight opening game, and Dimitrov grew in confidence from the opening four-minute test.
He had little trouble returning the Murray serve and, unlike the Briton's previous opponents, was able to dictate in the longer exchanges.
Pinned way behind the baseline, Murray began to make errors, and it was an ambitious backhand when forced out wide that saw the Scot drop serve in game four.
If that drew a murmur from the afternoon crowd on Centre Court, there were a few gasps when Dimitrov broke to love for a 5-1 lead and served out the set confidently after just 25 minutes.
With his mix of pace and spin, the backhand slice proving especially effective, Dimitrov was moving his man all over the court and pushing hard for the crucial second break.
Murray looked to his box in disbelief after a poor smash into the net at 3-3 made it 18 errors to just five from Dimitrov, and the pressure told when he sliced a backhand wide to fall behind again.
The match was now slipping away from the champion and he finally reacted, taking advantage of the first signs of edginess from his opponent to convert from 0-30 and get back on level terms.
Murray was still on the back foot, however, gasping for breath and urging the crowd to get behind him after winning a pulsating 31-stroke rally at 4-4, 30-30, and then fending off two break points at 5-5.
Reaching the tie-break might have felt like a minor victory for Murray, but Dimitrov was undeterred and again dominated the key moments, coming up with a backhand pass, a drop volley, and a terrific lunging backhand volley from 4-4.
Murray had recovered from two sets down at the same stage last year, but Dimitrov was a tougher proposition than Fernando Verdasco.
There was a sense of inevitability when the Briton double-faulted to drop serve in game six of the third set, and another double fault brought up two match points for Dimitrov two games later.
Murray saw off the first with the kind of forehand winner he had been searching for all afternoon, but he could only find the net moments later and his reign as champion was over.
"Today was one of those days when I was pretty steady for the whole match and came out the winner," said Dimitrov.
"It's tough when you know the person well outside the court and you have to face them. I have hopefully two more matches left and I am just focusing on that and trying not to get carried away."