The British duo defeated Christopher Kas and Sabine Lisicki in a thrilling champions' tie-break 10-7 after steamrolling the opening set 6-1 and dropping the second 7-6(9-7).
Earlier, Murray and Robson survived a scare before finally seeing off Australia to progress to the semis.
Murray has no intentions of taking it easy in the mixed doubles, despite his date with destiny tomorrow.
The pair beat Lleyton Hewitt and Sam Stosur 6-3 3-6 10-8 in just over one hour and 20 minutes on Centre Court.
And while he has more than an eye on his men’s final match-up against Federer, who he lost to in the Wimbledon final in four weeks ago, Murray says tomorrow will be the perfect end to his Olympics campaign.
“I just really wanted to win – both of us did. It was an emotional end to the match and she served great to give me a chance to control the net,” the British number one said.
“I’m glad we did because it would have been unfair if we hadn’t.
“I was telling her to take her time on her serve. When we went up 8-6, I said some words that she’s probably never heard before and I think that maybe settled us down before.
“It’s not my usual preparation for a five-set final with Roger Federer but I enjoyed it. This isn’t what I’d normally do. Tomorrow is the perfect end of the tournament for me.”
Murray and partner Robson – who lost in the second round of the women’s singles competition to Maria Sharapova – were handed a wildcard entry to the mixed doubles competition and are now guaranteed a medal.
“This is incredible. Just to be playing singles was brilliant but to be guaranteed a medal – I can’t believe it,” the Wimbledon girls’ 2008 champion said.
“I got to serve out the match in both games today. For once it went in, I just went for it and we won.
“I’m watching everything, including the guys winning the rowing and I just hope we can do it.”
Max Mirnyi and Victoria Azarenka of Belarus await after they beat Mike Bryan Lisa Raymond 3-6 6-4 10-7.
The American duo can still take bronze with a win over Germany, and Mike already has a taste of gold with twin brother Bob as the Bryans won men's doubles gold with a 6-4 7-6 win over France's Jo-Wilfried Tsonga and Michael Llodra.
The Bryan twins, who have won 11 grand slam titles together and took home the men's doubles bronze in Beijing, were handed the victory in a second set tie-break when Llodra ploughed the ball into the net.
It was the second US tennis gold of the day after Serena Williams stormed to victory in the women's singles final.
France also took home two medals, with Julien Benneteau and Richard Gasquet earlier claiming the men's doubles bronze with a 7-6 6-2 win over Spain's David Ferrer and Feliciano Lopez.