World No.15 Stefanos Tsitsipas was left searching for answers after suffering a shock straight-sets loss to unheralded Brit Cameron Norrie at the Hopman Cup.
Norrie, ranked 91st in the world, secured the 7-6 (10-8) 6-4 win in 107 minutes at RAC Arena in Perth.
Katie Boulter can secure the tie win for Great Britain with victory over Maria Sakkari in the women’s singles rubber.
Tsitsipas has been touted as a potential future grand slam champion following his stunning rise up the rankings in 2018.
But the 20-year-old struggled in the 27deg heat on Saturday, committing a host of unforced errors as his unfancied opponent cashed in.
With temperatures often hovering in the high 30s at the Australian Open, Tsitsipas’ limp display in Perth is a huge worry.
“It was tough to adjust from the very beginning,” Tsitsipas said.
“Cameron played really well, but I really felt uncomfortable, I don’t know why. Probably because of the weather conditions. The heat here – it’s a bit different. It’s tougher conditions than Dubai where I was preparing.
“I feel like I’m getting tired easily, which I’m not happy with because I’ve been working really hard in the off-season.”
The next singles match for Tsitsipas is against American Frances Tiafoe on Monday.
He then takes on Swiss great Roger Federer in a marquee clash on Thursday night.
Norrie arrived in Perth a week and a half ago to attend his cousin’s wedding in Dunsborough.
The 23-year-old said that had helped him adjust to the heat, and he was thrilled with his display against Tsitsipas.
“Just to get that first match under my belt and that first win feels great, especially in Perth Arena,” Norrie said.
“Both of us weren’t very match fit and haven’t played under the pressure for a few months now.
“I was just trying to play every point like it was the last.”