Five-time champion Roger Federer is out of the US Open after Bulgaria’s Grigor Dimitrov won a late-night thriller to finally beat the Swiss great.
Federer, 38, had won all seven of their previous meetings but unseeded Dimitrov fought back to win 3-6 6-4 3-6 6-4 6-2.
Federer, who needed treatment for a back injury in the latter stages, said: “I felt it the whole time, but I was able to play.”
Dimitrov, 28, faces Russian fifth seed Daniil Medvedev in the last four.
“Clearly in the end he was not at his best. I used every opportunity I had,” said the Bulgarian.
World number 78 Dimitrov’s shock win ensured there will be at least one first-time Grand Slam finalist on Sunday.
Third seed Federer, who lost to Australian John Millman in the last 16 last year, has now been knocked out of the US Open by players ranked outside of the world’s top 50 for the second successive year – after never previously having lost to one at Flushing Meadows.
Afterwards, the 20-time Grand Slam champion said he was struggling with the back problem throughout the match.
“I feel low. I’m disappointed it is over because I feel as I though I was playing well,” Federer said.
“It is a missed opportunity. I thought if I could get through I’d have two days off after.”
Federer’s exit leaves long-time rival Rafael Nadal as the strong favourite to lift the trophy, with defending champion Novak Djokovic also out after retiring injured from his last-16 match against Stan Wawrinka on Sunday.
Spanish second seed Nadal, a three-time US Open champion, faces Argentine 20th seed Diego Schwartzman in their quarter-final on Wednesday.
But it is clearly a golden opportunity for 33-year-old Nadal to win his 19th Grand Slam title and narrow the gap on Federer in the race to be regarded as the greatest men’s player of all time.
Federer’s loss also ended the possibility of the illustrious pair, rather remarkably, meeting at the US Open for the first time in their enduring rivalry.
Dimitrov, whose career has stalled spectacularly in the past two years, was not expected to be the man to prevent a ‘Fedal’ final from happening.
Nicknamed ‘Baby Fed’ in the early days of his professional career because of his technique, the Bulgarian was once heralded as the man who might succeed the Swiss as the leading player in the men’s game.
But he has tumbled down the ATP rankings since reaching a career-high ranking of three in November 2017, with a shoulder injury derailing his season this year and forcing him to withdraw from four tournaments.
Coming into the final Grand Slam of the season Dimitrov had lost seven of his previous eight matches, including a chastening defeat by world number 405 Kevin King in Atlanta.
However, the 2017 World Tour Finals champion has suddenly rediscovered his form at Flushing Meadows to devastating effect.
“I think the past six, seven months have been pretty rough for me,” he said.
“It was that low that I don’t even want to go there any more. It was just obviously injury, losing points, ranking. That’s the lowest point of any player.
“I kept on believing again in the work, the rehab I had to put behind my shoulder, the exercise, the practice. There were so many things I had to adjust.
“Next thing, you’re almost end of the year, you have a result like that. It’s pretty special to me.”
Dimitrov bounced back from losing the first set against Federer with ferocious forehands which rocked the Swiss and helped him level the match.
Despite falling behind for a second time, Dimitrov managed to retain belief and dragged his long-time foe into some physically-draining points in the fourth set.
Having broken in the opening game, Dimitrov pushed for a 5-2 lead in a remarkable eighth game where Federer fought off seven break points to eventually hold.
Federer then had five chances of his own to break back in another marathon game before Dimitrov served out to take the match into a decider, the Swiss then taking a 10-minute medical time-out in a bid to ease his back injury.
That did not alleviate the problem, however, Dimitrov taking full advantage to win a match ending at 23:46 local time after three hours and 12 minutes.
Earlier, Serena Williams underlined her tag as the favourite for the US Open with a brutal quarter-final win over China’s Wang Qiang in just 44 minutes.
The 37-year-old American broke serve five times and hit 25 winners as she eased to a 6-1 6-0 win over the 18th seed on Arthur Ashe Stadium
Williams, seeded eighth, is chasing a record-equalling 24th Grand Slam title.
She will face Ukraine’s fifth seed Elina Svitolina, who beat Britain’s Johanna Konta, in the semi-finals.
“When I play someone who is playing well I have to step up or go home and I’m not ready to go,” said Williams, who earned her 100th singles win at the US Open.
“I knew I needed to come out and play well. I’m feeling good, had a really tough year and I’m still here.
“Physically I’m feeling great and more importantly I’m having fun every time I come out here.”
Six-time US Open champion Williams has not won a Grand Slam title since returning from giving birth to daughter Olympia in September 2017.
She has fallen short of moving level with Australian Margaret Court’s all-time tally with defeats in the past two Wimbledon finals and last year’s US Open showpiece.
Here she has moved serenely through the draw, steamrolling three of her opponents – including old rival Maria Sharapova – in straight sets.
American 17-year-old Caty McNally is the only player to have tested Williams, trying to push her illustrious opponent around the court in a bid to expose her perceived lack of movement.
And that will be the tactic likely to be adopted by Svitolina, whose relentless returning is the hallmark of her game.
Williams never had that problem against Wang, keeping the points short with her thunderous serves and booming groundstrokes.
Williams dropped just seven points as she raced into a 5-0 lead, Wang avoiding the bagel with a hard-earned hold before another forehand winner from the American clinched the opener in 23 minutes.
Williams won 26 of the first-set points compared to 11 by her opponent, cracking 12 winners and winning 92% of the points when she landed her first serve.
Wang, who had not dropped a set on her way to the last eight, looked completed shell-shocked as she continued to be pummelled by a ruthless Williams in the second set.
The winners continued to flow from the American’s racquet as she did bagel Wang at the second attempt, sealing the shortest completed win of the tournament with another sizzling cross-court forehand.
Wang won just four points in the second set and ended the match without hitting a single winner.