London: World No. 3 Stan Wawrinka and world No. 6 Milos Raonic of Canada both crashed out in the opening round of the Aegon Championships at London's Queen's Club on Tuesday with temperatures reaching almost 38 degrees on court.
Second seed Wawrinka, runner-up in the French Open nine days ago, went down 7-6 (4), 7-5 to Spain's Feliciano Lopez.
Raonic, beaten in last year's Wimbledon final, lost to young Australian wildcard Thanasi Kokkinakis 7-6 (5), 7-6 (8).
Both men were below par in the fierce heat as they began preparations for this year's Wimbledon, which begins on July 3.
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 quarterfinals.
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 have 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."
Top seed and world No. 1 Andy 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 Jordan Thompson of Australia replaced him in the third match on centre court.
Thompson, 23, who is ranked 90th in the world, reached the final of the Surbiton challenger event last week. He and Murray have never previously played against each other.
British media reported that Murray will donate his winnings from the tournament - which could amount to almost £350,000 ($440,000) - to a fund helping victims of the Grenfell Tower fire in which more than 75 people have died.
The tower block is only a few kilometres away from the Queen's Club in west London.