Great Britain are one win away from the ATP Cup semi-finals after Dan Evans produced some of his best tennis to beat Alex de Minaur and level the tie with hosts Australia.
Evans sealed a thrilling 7-6 (7-4) 4-6 7-6 (7-2) win in three hours 24 minutes - the longest match of the tournament.
"I got through by the skin of my teeth," the 29-year-old said.
Jamie Murray and Joe Salisbury will take on De Minaur and Nick Kyrgios in the decisive doubles in Sydney.
Great Britain had earlier gone behind when a focused Kyrgios beat Cameron Norrie 6-2 6-2 in the opening singles rubber.
They slipped further behind when Evans went 3-0 down in the opening set against 20-year-old De Minaur but the Briton fought back against a player who is ranked 24 places above him at 18th.
The inaugural ATP Cup is a 24-nation knockout team tournament that has been set up by the men's professional tour to kick off the 2020 season.
'Phenomenal' Evans keeps Britain's hopes alive
British number one Evans, who upset world number 11 David Goffin to inspire the turnaround against Belgium in the group stage that kept his team in the tournament, once again showed he has the mettle and the shots to beat higher ranked opponents.
He put behind him a poor start to break back in the fifth game and took the first set on a tie-break when De Minaur netted.
The young Australian, who won three ATP titles last year, kept himself in the match by holding on to an early break to take the second set.
Evans had looked to be in charge of the third when he went 3-0 up but was then pegged back in what became an absorbing final set.
A time violation for Evans on his serve - given when it looked like he had already started his service motion - may have been playing on his mind to allow De Minaur a break back courtesy of a passing shot that was helped by the net cord.
Evans had four match points at 6-5 but a nerveless De Minaur saved them all with three emphatic winners and an ace to eventually force a tie-break.
With Kyrgios encouraging the home crowd to make even more noise with gestures from the bench, it was Evans who seemed to feed off the atmosphere, with a beautiful lob and stinging forehand winner at the net setting the tone as the Briton set up another four match points.
This time he converted without hesitation, wrapping up victory when De Minaur returned wide.
"He was phenomenal," Britain's captain Tim Henman said. "He kept fighting, I'm very, very proud of him."
Britain's fate is now in the hands of doubles specialists Murray and Salisbury, with Australia opting for a late change in their line-up for the decider.
The hosts will be counting on De Minaur and Kyrgios to shake off any weariness from the singles when they play instead of Chris Guccione and John Peers.