Great Britain are one win away from the Davis Cup Finals knockouts after Dan Evans fought back from a set and break down to put them ahead against France.
With a spot in the Final Eight at stake, Evans opened the best-of-three tie by beating Arthur Fils 3-6 6-3 6-4.
British number one Cameron Norrie will secure his team’s progress if he beats Ugo Humbert in the second singles.
If Norrie loses and France level, Evans and Neal Skupski can still clinch qualification in the deciding doubles.
Four nations – Britain, Australia, France and Switzerland – are playing in the group-stage event at Manchester’s AO Arena.
They all play each other once in a round-robin format, with the top two countries going through to the knockout stage of the men’s team competition – known as the ‘Final Eight’ – in Malaga in November.
With Australia already through and Switzerland eliminated, Britain know they can only qualify with a victory over the French.
Britain, who last won the Davis Cup in 2015, are aiming for a return to the knockout stage after missing out last year.
‘It’s never simple’ – Evans uses crowd energy to fight back
With a strong squad at his disposal, Great Britain captain Leon Smith had a tough selection call to make for the win-or-bust tie against a talented French squad.
Ultimately, he picked his highest-ranked players in Evans and Norrie, with former world number one Andy Murray and promising youngster Jack Draper missing out.
The move also ensured Evans – who would have played second if the lower-ranked Murray or Draper had been picked – could have a break before the potentially decisive doubles.
But French captain Sebastien Grosjean sprung a surprise by handing a Davis Cup debut to 19-year-old Fils – who is the highest-ranked teenager on the ATP Tour at 44th in the world.
The match-up did not initially look comfortable for world number 27 Evans.
Being pinned deep behind the baseline, Evans struggled for rhythm on serve and was unable to get on top in the rallies as Fils dominated with his athleticism and power.
Things looked ominous for Evans when he trailed by a set and a break.
But the energy returned when he ended a run of losing five games in a row and, backed by a British Davis Cup record crowd of 13,000, that sparked a magnificent turnaround.
Evans strung together a winning sequence of seven games to take the second set and break early in the third, going on to convert his second match point when Fils hit a forehand into the net.
“That’s something with the Davis Cup, it is never ever simple,” Evans said.
“He played very good at the start, [he has] a very unorthodox forehand – a good one but different. It took me a while to get into it and I was a bit flat.
“Leon said let’s throw the gameplan out of the window, bring anything and everything to the court, including the crowd.
“I fought my way through the second set and played some very good stuff in the third when I got my game back.”