Jamie Murray and Heather Watson levelled the Battle of the Brits team event going into the final day after a thrilling win in the mixed doubles.
Murray and Watson, playing for the Union Jacks, won 6-3 3-6 17-15 against British Bulldogs pair Liam Broady and Harriet Dart in Roehampton.
The Union Jacks have trailed throughout the week-long competition, but are now level at 45-45 going into Sunday.
The first team to reach 60 points will triumph at the National Tennis Centre.
“The match tie-break was brutal, it was pretty much neck and neck the whole way,” said 34-year-old Murray.
“Heather served great and came up with some clutch returns, I was just trying to stay as calm as I could.
“It is the first time we’ve been level since we started on Monday morning so we’re happy to go into Sunday with a chance to win.”
There will be 12 matches played on ‘Super Sunday’, where points will be worth more in a format set up to provide an exciting conclusion.
The country’s leading men and women are playing together in singles, doubles and mixed doubles matches in the unique team event.
It has been organised by Jamie Murray to provide competitive action for British players while the professional tours remain suspended because of the coronavirus pandemic.
Norrie retires injured before Andy Murray wins
British number three Cameron Norrie pulled out of his singles match against Dan Evans through injury.
Norrie, 24, trailed 4-0 in the first set before retiring with a hip problem, deciding not to risk making it worse with the professional tour resuming this month.
Andy Murray continued his own preparations with a win in the men’s doubles which set up the chance for his older brother Jamie and Watson to level.
Former world number one Murray, 33, won 4-6 6-3 10-4 alongside Lloyd Glasspool in their match against Kyle Edmund and Joe Salisbury.
Murray is only competing in doubles as he continues to build up his fitness, with the Scot planning to play in the Cincinnati Masters and US Open double header in New York later this month.
Earlier, Katie Boulter, Jan Choinski and Jodie Burrage all won their singles matches for the Jacks.
The Bulldogs, who led 41-32 overnight, added to their tally through former world number 14 Edmund, then Dart and Beth Grey in the women’s doubles.
Union Jacks 45-45 British Bulldogs (first to 60)
(Matches show Union Jacks players first)
Katie Boulter 6-1 6-1 Beth Grey (2pts)
Anton Matusevich 2-6 1-6 Kyle Edmund (2pts)
Dan Evans 4-0 ret. Cameron Norrie (3pts)
Alicia Barnett/Olivia Nicholls 2-6 2-6 Harriet Dart/Beth Grey (2pts)
Andy Murray/Lloyd Glasspool 4-6 6-3 10-4 Joe Salisbury/Kyle Edmund (2pts)
Jamie Murray/Heather Watson 6-3 3-6 17-15 Liam Broady/Harriet Dart (3pts)
Jan Choinski 6-4 4-6 10-4 Alastair Gray (1pt)
Jodie Burrage 2-6 6-2 10-7 Emma Raducanu (2pts)