Andy and Jamie Murray edged Great Britain closer to a first Davis Cup final in 37 years on Saturday while Argentina were within sight of their fourth final spot since 2006.
The Murray brothers thrilled their home Glasgow crowd by defeating Australia's Lleyton Hewitt and Sam Groth 4-6, 6-3, 6-4, 6-7 (6/8), 6-4 in a gruelling four-hour rubber.
Victory gave the home side a 2-1 lead and it means Andy Murray can now clinch the tie for Great Britain in Sunday's first reverse singles as they attempt to win the competition for the first time since 1936.
The 28-year-old will secure a final showdown against either Belgium or Argentina in November if he defeats scheduled opponent Bernard Tomic.
If he loses, British world number 300 Dan Evans is due to face teenager Thanasi Kokkinakis in what would be the decisive second reverse singles.
"It was an incredible match and we had to come back from the disappointment of losing the fourth set," two-time Grand Slam winner Andy said.
"We stuck together like brothers should and managed to come up with enough good returns. It was as emotionally draining as much as it was physically."
Australia, 28-times winners of the tournament, had been looking to reach their first final since 2003.
"Davis Cup doubles over five sets can sometimes only rely on one or two points," said Hewitt, who is featuring in his final Davis Cup campaign.
"Doubles is always crucial but there is still two matches to go and we have to come up with the best plan to win those matches and give ourselves an opportunity to go through to the final."
Argentina are also dreaming of a return to the Davis Cup final after finishing runners-up in 1981, 2006, 2008 and 2011.
Carlos Berlocq and Leonardo Mayer edged Steve Darcis and Ruben Bemelmans 6-2, 7-6 (7/2), 5-7, 7-6 (7/5) to take the South Americans into a 2-1 lead over Belgium ahead of Sunday's reverse singles in Brussels.
Belgium's world number 15 David Goffin will face Mayer first-up on Sunday with Darcis scheduled to face Federico Delbonis in what could be the deciding rubber.
Argentina took Saturday's clash on a second match point after a Darcis return went long.
In the World Group play-offs, where the eight winners will play in the elite section next year, all the ties remained undecided going into the final day.
Thiemo de Bakker and Matwe Middelkoop stunned Roger Federer and Marco Chiudinelli 7-6 (9/7), 4-6, 4-6, 6-4, 6-1 to keep the Netherlands in the tie against Switzerland in Geneva after they lost both of Friday's opening singles.
"I think we played very well for four sets," said world number two Federer.
"They had a good tiebreaker and a good 10 minutes at the end of the fourth and the beginning of the fifth and they deserved victory in the end. Indoor doubles is brutal."
The Czech Republic, who were back-to-back champions in 2012 and 2013, opened a 2-1 lead over India in New Delhi after Adam Pavlasek and Radek Stepanek defeated favourites Rohan Bopanna and Leander Paes 7-5, 6-2, 6-2.
The United States, the record 32-time champions, took a 2-1 lead over Uzbekistan in Tashkent with Steve Johnson and Sam Querrey easing past Farrukh Dustov and Denis Istomin 6-3, 6-2, 6-2.
Colombia, Germany, Croatia, Italy and Poland were also in the driving seat in their play-offs.
In Odense, Rafael Nadal claimed a 21st straight win in Davis Cup when he teamed with Fernando Verdasco to defeat Denmark's Thomas Kromann and Frederik Nielsen, 6-4, 3-6, 7-6 (7/4), 6-4.
The victory gave five-time champions Spain a 3-0 winning margin over the hosts and prevented the embarrassment of relegation to Europe/Africa Group Two.