It took them a while to realise but Greece's Hopman Cup title hopes are hanging by a thread.
But Greece's shock 2-1 loss means they now must beat Switzerland and the US to have a chance of reaching the Hopman Cup final.
Tsitsipas was left searching for answers after suffering a 7-6 (10-8) 6-4 defeat to world No.91 Norrie.
Sakkari beat Boulter 6-0 4-6 6-2 in the women's singles rubber to level the tie.
But Great Britain prevailed 4-3 3-4 4-3 in the deciding mixed doubles, prevailing on the winner-takes-all point in the third-set tiebreak.
Under new Hopman Cup rules, the tie breaks are a first-to-five contest.
If the tiebreak is level at 4-4, the next point wins.
That is what occurred on Saturday, with Tsitsipas sending his backhand into the net to hand Great Britain victory.
After the match, Sakkari revealed she didn't initially know the match was over, thinking that a two-point lead in the tiebreak was necessary to secure victory.
"I thought we had one more point. After I saw them celebrating (I realised)," Sakkari said.
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 27-degree heat during his singles clash, 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.
"Both of us weren't very match fit and haven't played under the pressure for a few months now," Norrie said.
"I was just trying to play every point like it was the last."