His seasoned opponents, both former prime ministers, were cynical enough to appropriate the gist of his reformist zeal into their own sketchy party manifestos. Mr Khan has conceded in public that a victory now "would be a miracle" and that his Movement for Justice (Tehreek-i-Insaaf) Party "may not even win a single seat".
While local newspaper headlines gloated yesterday over new accusations that Mr Khan had once slapped Sita White, the heiress whose paternity suit against him in Los Angeles has made their alleged illegitimate daughter one of the hottest topics of this race, Mr Khan has retreated to campaign in the Northwest Frontier province of Swat.
The conservative Pathans there welcome him as a clan brother and his admiration for their ethos has become obvious, at least since his mid- life crisis, when he gave up his Armani suits for traditional tunics and baggy trousers.
Mr Khan's recent book, published in Urdu, extolled the austere life of Pathan warriors and advocates their code of honour.
But by suggesting that offenders who steal from the nation ought to be executed, the Oxford graduate has stunned the country's intelligentsia. Many now feel his best chance of success as a mainstream politician lies in distancing himself from religious extremists.
Ms White dropped her plan to confront Mr Khan in Pakistan over his denial of fathering Tyrian Jade, aged four. But yesterday she denounced him from California in an interview with The Nation, an English daily, published in Lahore.
"He was the father, " she said. Her earlier allegations that he had tried to talk her into an abortion because the baby was not male damaged Mr Khan's popular image as a man committed to Islamic ideals.
Mr Khan countered her attack by proxy through his young British wife, Jemima, who extolled his virtues on television and dismissed the "salacious reports" as "above all, so un-Islamic. No one benefits from reading this nonsense," she said. Mrs Khan, 22, had left her baby, Sulaiman, with his nanny while she addressed two women-only rallies in her halting Urdu.
In the interview in The Nation, Ms White described in detail how she had provoked the aspiring prime minister by berating his hunting prowess. She recounted how Mr Khan crossed in front of a friend during a shooting expedition and bagged the bird for himself. "We were all discussing it. Imran had fired past him. Then Imran actually slapped me across the face in front of everybody. I was just in shock. I had never seen that side of his personality."
Afterwards, Mr Khan reportedly told his stricken girlfriend: "Even if the tiger is wrong, you should say that he is right." Ms White dismissed reports in the London papers that she was jealous of her replacement in Imran's affections. "I don't know Jemima," she said. "She seems very young and innocent, and easy to push around. I feel sorry for her."
Naseem Zehra, the spokeswoman for Mr Khan's party, said: "We think this whole Sita White business is tacky. The timing is vicious. We do not want to comment."
Tonight, the candidate will fly home for the final innings before the vote. Mr Khan's followers accuse Nawaz Sharif, who most analysts believe will win the election, of manipulating Sita White into timing her embarrassing paternity suit for the election campaign. But a spokesman for Mr Sharif's Pakistan Muslim League shrugged this off, saying: "If Imran's past catches up with him, we are not to blame."