Henman was defeated by Todd Martin, the American No 13 seed, 7-6, 7-6, 6-4, in a contest which produced only one break of serve but four separate breaks in play because of rain.
Sampras, who had been left teetering overnight, two sets to love down against Richard Krajicek, was unable to disturb the Dutchman's concentration when their match resumed. Krajicek, unseeded even though ranked No 13 in the world, continued to pound down his serves, and broke the world No 1 in the seventh game to complete his victory, 7-5, 7-6, 6-4.
Ivanisevic, two sets to one down overnight, was defeated by the Australian Jason Stoltenberg, 6-3, 7-6, 6-7, 7-6. In the fourth set, Ivanisevic had three break points in the second game, Stoltenberg two in the 11th, and the Australian dominated the tie-break, 7-3.
All of which leaves Martin on his Todd as the only seed in the semi-finals. It is the first time for 30 years that three of the last four men have been unseeded (Boris Becker, in 1985, is the only unseeded champion) and a new name is guaranteed to be inscribed on the trophy.
In the semi-finals, Krajicek plays Stoltenberg and Martin faces his compatriot MaliVai Washington, who defeated Alex Radulescu, the Romanian-born German, 6-7, 7-6, 5-7, 7-6, 6-4.
Krajicek, notorious for once saying that the majority of women players were "lazy fat pigs", has ensured that he will remembered for something rather more positive.
Stoltenberg, ranked No 46, is the first Australian semi-finalist since Pat Cash won the title in 1987.
Sampras, on the evidence of his experience in the quarter-finals, would not be surprised if Krajicek succeeds him.
"I think he's got a good chance if he serves and returns like he did today and yesterday," Sampras said. "His return was the shot that surprised me. His return and passing shots off his backhand really caught me off guard.''
At the same time,Sampras rued the missed chances that cost him his first defeat in 26 matches at the All England Club. "The difference is pretty slim," he said. "I was in inch away from winning the second set. I just didn't win the big points today or yesterday, and he played very well.''
Sampras and Krajicek arrived on the Centre Court when the spectators were still absorbing Henman's performance against the unspectacular but rock-steady Martin. Henman's coach, David Felgate, put the defeat in perspective when he said, "It's no disgrace losing to him. He lost to a better player, a more mature player.''
Henman added: "There was only one break in the whole of the match. There were chances there that unfortunately I didn't take. But, having said that, I think I lost to the better player on the day.''
While disappointed not to have advanced to the last four, as Yorkshire's Roger Taylor did 23 years ago, Hen man said: "I can reflect on the past ten days as the greatest tournament of my career so far, and I hope that I have many more good Wimbledons, and better ones, in the future.''
The 21-year-old from Oxford saved two break points before the majority of the spectators had arrived. He relieved the situation with a forehand volley and an unreturnable serve, ended the opening game with an ace.
Having dealt efficiently with this early assault, Henman attacked Martin's serve. He was assisted by an overrule by the umpire, Britain's Gerry Armstrong, after a deep backhand down the line had been called out at deuce in the fourth game, but had no answer to Martin's serve on the break point.
Two consecutive aces enabled Henman to hold to love in the fifth game, after which Martin missed a lob in an attempt to parry a drive, and Henman prepared for his second opportunity to break. On this occasion, the American produced such a pacey volley on the backhand that his opponent was left with little option but to net his forehand response.
Henman continued to play the more enterprising tennis, and was rewarded with his first set point when leading 5-4. A confident return at 30-30 resulted in Martin mistiming a backhand half-volley long.
The chance went before Henman was able to put a racket on the ball. Although Martin's first serve was called out by the centre line judge, the umpire overruled and it counted as an ace.
Henman's returns created two more set points at 6-5. Martin saved the first with a serve which his opponent could not keep in play and the second with another winning delivery, this time to the backhand.
"When he's serving as big as he was," Henman reflected, "first and foremost I had to try to put the ball back in play, which unfortunately I couldn't do.''
After those promising moments, the tie-break appeared to be running away from Henman at 2-5, but he recovered impressively to level at 5-5. At that point, Martin powered down his third ace, and Henman double-faulted when trying to save the set.
He did not look comfortable when tossing the ball for the second serve in the blustery conditions, but went through with the delivery, which landed long. We're all prone to double-faults," Henman said afterwards. "Maybe I shouldn't have hit the ball when it was blowing about in the wind, but I served it and missed it.''
Henman saved two break points in the second set. On the first occasion, in the fourth game, Martin hit a forehand return over the baseline - just.
Play was interrupted for an hour and 26 minutes, with Martin leading 4-3 on serve, before the American's second opportunity to break came in the eighth game. Henman put a backhand half-volley wide on the third deuce point, and was relieved to see another of Martin's backhand returns land long.
The American whipped through the second tie-break, allowing Henman only two points - one of them a double-fault - before serving out with an ace.
Finally, between the second and third rain delays, we saw the only break. Unfortunately for the partisans, it went against Henman in the fifth game of the third set. Although the Briton saved two of the points against him at 0-40, with an ace and a service winner, Martin passed him on the third with a backhand off a second serve.
Incidentally, on the last occasion that there were three unseeded semi- finalists, in 1967, Britain's Roger Taylor lost to Germany's Wilhelm Bungert, and Nikki Pilic was beaten by John Newcombe, the No 3 seed, who defeated Bungert in the final.
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