Singh was asleep when P C Alexander, Principal Secretary to the Prime Minister, rang him up frantically to convey Rao's decision to appoint him as Finance Minister.
"The decision was out of the blue", Singh is quoted as having said by his daughter Daman Singh in her book "Strictly Personal: Manmohan and Gursharan", which covers the years prior to his becoming the Prime Minister in 2004.
The book is based on Daman's conversations with her parents and hours spent in libraries and archives.
According to Singh, Rao's most important role was that he allowed the process of liberalisation and opening up to go ahead, and gave it his full support.
Singh says Rao was first a little sceptic about the liberalisation idea and had to be persuaded.
"I had to persuade him. I think he was a sceptic to begin with, but later on he was convinced that what we were doing was the right thing to do, that there was no other way out. But he wanted to sanctify the middle path - that we should undertake liberalisation but also take care of the marginalised sections, the poor," recounts Singh.
Referring to the imposition of Emergency in 1975, Daman says it came as a surprise to her father.
"Well, it was a surprise. There had been unrest, but nobody expected that Mrs Gandhi would go that far," she said.
When his daughter asked him how the Emergency affected the government servants, Singh replied, "I think there was a lot more emphasis on punctuality, on discipline. So some good things happened."
After the Morarji Desai-led Janata Party won a majority and came to power post-Emergency, a number of officers were shunted out but Singh kept his job.
Initially, Singh felt Desai was not quite fond of him.
"When Morarji Desai became prime minister he had been told that I was close to the previous government. So he was quite rude to begin with. But after some time, he became very fond of me. Morarji Desai was fairly balanced, although people misunderstand him as a very rigid man. I think on the surface he was rigid, but he was amenable to persuasion," Singh is quoted as saying.