Cameron Norrie defeated Greek world number 15 Stefanos Tsitsipas in straight sets to inspire Great Britain to victory in the opening tie of the Hopman Cup in Australia.
World number 91 Norrie, 23, secured the biggest win of his career with a 7-6 (10-8) 6-4 victory over Tsitsipas.
Team-mate Katie Boulter, 22, was beaten 6-0 4-6 6-2 by Maria Sakkari in the women's singles rubber.
But the Britons won the mixed doubles 4-3 3-4 (2-5) 4-3 (5-4) to win the tie.
The Hopman Cup, played in Perth, comprises two singles matches and a mixed-doubles contest between nations in a round-robin format with two groups of four.
Norrie and Boulter will face Switzerland's Roger Federer and Belinda Bencic on Sunday before playing Serena Williams and Frances Tiafoe of the USA on Thursday.
The winners of both groups will contest Saturday's final.