World No 1 Andy Murray, Stan Wawrinka and Milos Raonic crashed out in the opening round of the Aegon Championships at London's Queen's Club on Tuesday as the top three seeds all suffered embarrassing upsets.
With temperatures reaching almost 38 degrees on court, Murray, a twice Wimbledon champion, was beaten 7-6(4), 6-2 by Australian world number 90 Jordan Thompson.
Second seed and world number three Wawrinka, runner-up in the French Open nine days ago, went down 7-6(4), 7-5 to Spain's Feliciano Lopez.
Third seed Raonic, beaten in last year's Wimbledon final by Murray, lost to young Australian wildcard Thanasi Kokkinakis 7-6(5), 7-6(8).
All three favourites were below par in the fierce heat as they began preparations for this year's Wimbledon, which starts on July 3.
Their shock exits left World No 7 Marin Cilic, the 2012 Queen's champion, as the highest seed left in the tournament. Murray faced a new opponent for the opening match of his Queen's title defence after fellow Briton Aljaz Bedene withdrew with a wrist injury.
Lucky loser Thompson replaced him in the third match on centre court but penned an astonishing upset.
Thompson, 23, reached the final of the Surbiton challenger event last week, but took the first set on a tiebreak and then raced through the second.
"Andy's the world number one - I've looked up to him and that's definitely the biggest win of my career. I took each point at a time. I didn't expect it to be winning in straight sets," he told the BBC.
"I was sitting around yesterday hoping to get a match. Here I am, I got in the draw and I was so lucky to be here. I don't know if I can say my immediate thoughts."
After his defeat by Rafael Nadal in the Paris final, Wawrinka added Paul Annacone to his coaching team as a grass court specialist.
The American had previously coached Roger Federer and Pete Sampras, who between them have taken 14 Wimbledon titles.
Swiss Wawrinka hopes Annacone will improve his prospects at Wimbledon, where he has never progressed beyond the quarter-finals.
He was below his best on Tuesday as Lopez produced some deft touches to support his big serve.
"I came here with a lot of confidence and tennis is a lot about confidence," Lopez told the BBC.
Raonic said he would spend time on the practice court and in the gym after his defeat by Kokkinakis.
It was the Australian's first win over a top 10 player as he began the long road back from playing only one match in 2016. A series of injuries over the past two years had sent his ranking to 993 from 69.
"I've been out of the game for so long, it's huge for me," the 21-year-old, now ranked 698, said.
"I'm trying to look forward now and get myself going week by week, and I can't wait to play my next round."