Nick Kyrgios and Jordan Thompson gave Australia an unexpected 2-0 lead after the first day of their Davis Cup quarter-final against the United States in Brisbane on Friday.
The unheralded Thompson stunned world number 15 Jack Sock in four sets in the opening rubber before Kyrgios saw off the big-serving John Isner 7-5, 7-6 (7/5), 7-6 (7/5).
Only 10 times in Davis Cup history has a country come back from being 0-2 down to win a tie, the most recent when Croatia recovered to beat the US at this stage last year.
"We've been up two-zero before and ended up losing, so we know it takes three (rubbers) and tomorrow's a new day," US captain Jim Courier said.
"We're certainly not happy with the score but we're professionals and we'll be ready to play tomorrow."
Kyrgios was superb against Isner, a tough opponent who has one of the biggest serves in world tennis.
The controversial Australian pushed Roger Federer to the brink in Miami last week and he carried that form into Friday's match.
Despite a slow start when he went down 3-0 in the opening set, Kyrgios recovered quickly and was always slightly on top of Isner.
He read the American's serve brilliantly and had the edge from the baseline, coming back from 2-5 down in the third set tiebreak to take a high quality match in two hours, 25 minutes.
Kyrgios credited his recent good form with a change in attitude on court.
"I'm trying to knuckle down and compete for every point and that's something I haven't done in the past," he said.
"My level's always been there but my mentality is a lot better.
"I'm still very emotional out there. I'll still challenge the umpire, I'll still say what I think, I'll still throw my racket, I'll still swear, but I'll compete every point.
"I think I'm only human so I'm not going to change in that department."
Earlier Thompson, ranked 79th in the world, held his nerve to see off a faltering Sock 6-3, 3-6, 7-6 (7/4), 6-4 in front of a raucous crowd on Pat Rafter Arena.
Playing only his second Davis Cup tie, Thompson, 22, went into the match against the American number one as the huge underdog.
He struggled to stay with Sock in the opening set but seized his chance when the American's serve deserted him at 3-4, breaking Sock to win the opener in 37 minutes.
Sock found his range with his booming forehand and stormed back to take the second.
The American number one looked the more dangerous in the third but Thompson held on to force a tiebreak, gaining a vital break before taking the set when Sock double-faulted.
Thompson carried all the momentum with him into the fourth set against an increasingly tired looking Sock and closed out the match in three hours.
"He played a good match -- he deserved to win," a disappointed Sock said.
"He served well, made a lot of balls."