Cash, effectively sidelined from the tournament scene for the past two years through injury, beat the veteran Christo van Rensburg 7-5, 6-2 to keep Australia in the tie and then linked up with Kristine Radford to win the decisive doubles 7-6, 7-6.
The South African pairing of Van Rensburg and Amanda Coetzer were expected to possess too much doubles experience, but Cash's remodelled serve helped clinch a fluctuating second set tie-break 11-9 and give the unseeded Australians a 2-1 winning margin.
The 1987 Wimbledon champion, now 29, underwent back surgery last year after previous lay-offs with knee and Achilles tendon problems, yet insists he will be back beating the world's best before the end of the year.
"I was a bit nervous. There was a big crowd and it was the first time I've played in Australia for a while," Cash said. "It's been a long hard slog but I feel good."
Cash's determination to regain his fitness was underlined in pre-Christmas tests in London when he registered a body fat reading of just seven per cent and the best endurance result he has produced in his career.
His reflexes are still sharp too, an improbable volley setting up the vital break for 4-2 in the second set which decided his tussle with the 32-year-old Van Rensburg.
The South African did not help his cause with seven double faults and was even more profligate in the final rubber, giving Cash and Radford crucial assistance at key moments.
Australia will be hoping for a similar result when they travel to South Africa for the first round of the Davis Cup next month but their immediate task will be to upset the top-seeded Czech Republic in tomorrow's quarter-final.
If they are to have a chance, Radford will need to improve after being thrashed 6-1, 6-1 in just 57 minutes by the world No 18, Coetzer, in the opening women's singles.