Patten and Heliovaara saved five set points in a thrilling first-set tie-break and had a chance of their own at 7-6, only for the Australians to win three successive points to move ahead in the match.
But Patten and Heliovaara, with the majority of the crowd cheering loudly at every success, fought hard and held off the first of the match points in the 12th game of the second set.
They also then saved two further match points in the tie-break, fighting back from 7-6 and 8-7 behind to take it 10-8 and force a deciding set.
Neither pair could break serve as a 10-point tie-break to settle the match always seemed inevitable.
Purcell and Thompson led 8-6, but Patten and Heliovaara won five of the next six points to seal an incredible victory, one which was marked by a near-deafening roar from a delighted Centre Court audience.
