Amid protest from the PMO, the Post published a correction with regard to quotes attributed to the Prime Minister's former media adviser Sanjaya Baru and political historian Ramachandra Guha.
An earlier version of this article failed to credit the 'Caravan', an Indian magazine, for two statements that it originally published in 2011.
"The assertion by Sanjaya Baru, a former media adviser, that Singh had become an object of ridicule and endured the worst period in his life first appeared in the 'Caravan', as did an assertion by Ramachandra Guha, a political historian, that Singh was handicapped by his 'timidity, complacency and intellectual dishonesty'."
"While both men told The Post that the assertions could accurately be attributed to them, the article should have credited the 'Caravan' when it used or paraphrased the remarks. The article has been updated," said the correction.
The correction came as Pankaj Pachauri, Communications Adviser to the Prime Minister, wrote a strong protest letter to the US-based newspaper, saying the article reflected "unethical and unprofessional conduct" on part of journalist Simon Denyer.
Pachauri referred to quotes attributed to Baru and said Denyer had 'rehashed and used' an eight-month-old quote from an Indian magazine.
Terming the story as "totally one-sided", Pachauri said the journalist "never" got in touch with the PMO for its version on the article. "We expected better from the correspondent of the Washington Post for fair and unbiased reporting," he said.
Meanwhile, Tushar Poddar, India Economist of Goldman Sachs, also distanced himself from the comments attributed to him in the article.
In an email to the daily, Poddar said, "I was dismayed to read ...Comments attributed to me about India's Prime Minister Manmohan Singh. These published remarks bear little or no resemblance to my recollection of a conversation I had with your correspondent several months ago."
In his letter, Pachauri has complained that Denyer, "despite all lines of conversations open", never "got in touch with us for our side of the story though you regularly talk to me about information from the PMO. This story thus becomes totally one sided."
Pachauri referred to Denyer's mention that his request for an interview with the PM was declined and said his mail had clearly stated that the interview was declined 'till the monsoon session' of Parliament which gets over tomorrow.
In its rejoinder, the PMO spokesman wrote to Denyer "you have been telling the media here in India that your request for an interview was declined though the mail below says clearly that the interview was declined 'till the monsoon session' of Parliament which gets over in two days.
"When I rang you up to point this out, you said sorry twice though you tell the media here that you never apologised.
"Your website, where we could have posted a reply is still not working, 11 hours after you said sorry the third time for its inaccessibility," Pachauri said.
Responding to this, Denyer wrote on the Post "when I made my final request for an interview with the PM in July, I was told on Jul 30 'The PM has declined all interview requests till the monsoon session is over.' At that stage, the current session of parliament (known as the monsoon session) of parliament had not even begun. There was no mention of the possibility of an interview afterwards."
He said his "apology was for the fact that the website was down and the PM's office could not post a reply directly. As soon as the problem was fixed, I informed them. I stand by the story."