Great Britain's hopes of reaching the United Cup semi-finals rely on Katie Boulter beating five-time major champion Iga Swiatek after Billy Harris narrowly lost to former Wimbledon semi-finalist Hubert Hurkacz.

Harris, 29, pushed 16th-ranked Hurkacz in the opening match of the best-of-three tie before going down 7-6 (7-3) 7-5 in Sydney.

The late-blooming Harris, who is ranked 125th in the world after making huge strides in the past two years, was aiming to give Britain a platform to reach the last four with the biggest win of his career.

His defeat means 28-year-old Boulter must beat Swiatek later on Thursday to tee up a deciding mixed doubles match.

Harris has been playing as Britain's leading man in the mixed gender team event with Jack Draper nursing a hip injury and Cameron Norrie playing an ATP event in Hong Kong.

While he served strongly, Harris was unable to break Hurkacz and fell short in the decisive moments.

A tight first set saw neither player face a break point until the Briton fought off two opportunities for Hurkacz in a tense 12th game, eventually hanging on to his serve to force a tie-break.

A costly error from Harris - a miscue long with an overhead - handed an early mini-break to Hurkacz, whose pedigree at the highest level was demonstrated by the way he clinically secured the lead.

Despite falling behind, Harris showed his mental toughness in the second set. He reset quickly to create three break points in the second game, only for Hurkacz to fight back from 0-40 with five huge serves getting him out of trouble.

Harris was eventually broken when Hurkacz pounced for a 6-5 lead and, with the wind taken out of the Briton's sails, the 27-year-old Pole quickly wrapped up victory with a hold to love.

"I am super pleased, it was a difficult battle with Billy," said Hurkacz, whose run to the Wimbledon semi-finals in 2021 is his best performance at a major.