Although American media had widely speculated that Armstrong would admit to cheating in the interview on Monday, neither Winfrey nor Armstrong would confirm the report in the USA Today reported, in which the newspaper cited an anonymous source.
"We are not confirming any specific details regarding the interview at this time," a spokesperson for Oprah's network OWN told Reuters.
The report did not say which drugs Armstrong admitted to using, and the American's attorney and his spokesman did not immediately respond to requests for comment.
Armstrong (41) has always vehemently denied using performance-enhancing drugs and had never tested positive to a doping test. But the evidence against him has been overwhelming.
Oprah, on Twitter, offered little more herself other than to say Armstrong came prepared for the interview, which will be broadcast on Thursday.
"Just wrapped with @lancearmstrong More than 2 1/2 hours. He came READY," Winfrey tweeted.
But the television host hinted she would provide some more snippets, confirming she would appear on CBS television on Tuesday morning to talk about the interview.
CBS reported Armstrong indicated he might be willing to testify against others involved in illegal doping and was in talks about repaying part of the state funds he earned during his career.
The unconfirmed reports about his admissions followed Armstrong's apology to the staff of the cancer foundation he had started over difficulties they may have experienced because of the doping controversy.
"He had a private conversation with the staff, who have done the important work of the foundation for many years," said Livestrong Foundation spokesperson Katherine McLane.
"It was a very sincere and heartfelt expression of regret over any stress that they've suffered over the course of the last few years as a result of the media attention," she said.
Shortly after, Armstrong joined his legal team to meet with Winfrey for an interview described as "no-holds-barred".
The interview was supposed to take place at Armstrong's Texas home but was switched to a hotel in downtown Austin after news crews camped outside his house before dawn.
Swift fall from grace
A former cancer survivor who went on to become the greatest cyclist the world has seen, Armstrong's fall from grace has been as swift and spectacular as his rise through the French alps.
Long dogged by accusations he cheated his way to the top, an October report from the US Anti-Doping Agency (Usada) ultimately triggered his rapid slide.
Usada exposed Armstrong as a liar and a cheat, describing him as the ringmaster of the "most sophisticated, professionalized and successful doping program that sport has ever seen," involving anabolic steroids, human growth hormone, blood transfusions and other doping.
Former Armstrong teammates at his US Postal and Discovery Channel outfits, where he won his seven successive Tour titles from 1999 to 2005, testified against him as well as admitting to their own wrongdoing.
The mountain of evidence was overwhelming, and when Armstrong decided not to fight the charges against him, his Tour de France victories were quickly nullified. He was banned from cycling for life.
His sponsors, which had remained loyal to him, began deserting him and he stood down as chairman of Livestrong. Legal issues began to mount.
His former teammate Floyd Landis, a self-confessed cheat, filed a lawsuit against him for defrauding the US government, while the London-based Sunday Times is suing Armstrong to recover about $500 000 it paid him to settle a libel lawsuit.
Armstrong could also be forced to pay back amounts including $7.5-million to SCA Promotions, a Dallas-based company that paid him a bonus for his Tour de France wins.
Throughout it all, Armstrong remained silent, unrepentant and seemingly unconcerned as the cycling world was left reeling by the revelations.
That was until last week, when he announced he had agreed to an interview with Winfrey, prompting speculation he was ready to confess he cheated. – Reuters
Chronology of doping denials 2001
Armstrong spent over a decade vehemently defending himself against a litany of doping allegations. His reported confession on Monday came only after the testimony of others had forever tainted his cycling legacy.
Below are some of Armstrong's doping denials since 2001.
"This is my body and I can do whatever I want to it. I can push it, and study it, tweak it, listen to it. Everybody wants to know what I'm on. What am I on? I'm on my bike, busting my ass six hours a day. What are you on?" – Advertisement for Nike, July 2005
"I'll say to the people who don't believe in cycling, the cynics and the sceptics. I'm sorry for you. I'm sorry that you can't dream big. I'm sorry you don't believe in miracles. But this is one hell of a race. This is a great sporting event and you should stand around and believe it. You should believe in these athletes, and you should believe in these people. I'll be a fan of the Tour de France for as long as I live. And there are no secrets – this is a hard sporting event and hard work wins it. Vive Le Tour." – After Armstrong's seventh and final Tour de France victory August 2005
"I have never doped, I can say it again, but I have said it for seven years – it doesn't help." – On CNN's Larry King Live after French newspaper L'Equipe reports tests on urine samples taken from Armstrong during the 1999 Tour and frozen were positive for blood-boosting erythropoietin.
" ... the faith of all the cancer survivors and almost everything I do off of the bike would go away too. Don't think for a second I don't understand that." – In testimony under oath during legal proceedings involving SCA Promotions over a bonus payment for a Tour de France victory.
"I was on my death-bed. You think I'm going to come back into a sport and say, 'OK, OK doctor give me everything you got, I just want to go fast?' No way. I would never do that." – Speaking of his life in an interview in Aspen with Bob Schieffer, a respected journalist with CBS and a cancer survivor.
"The critics say I'm arrogant. A doper. Washed up. A fraud. That I couldn't let it go. They can say whatever they want. I'm not back on my bike for them." – Nike "Driven" commercial in the buildup to Armstrong's first Tour de France since his comeback from retirement, showing Armstrong training in a Livestrong jersey juxtaposed with images of cancer patients.
"It's our word against his word. I like our word. We like our credibility. Floyd lost his credibility a long time ago." – Response to disgraced cyclist Floyd Landis's accusations of systematic doping in the US Postal cycling team.
June 13 2012
"I have never doped, and, unlike many of my accusers, I have competed as an endurance athlete for 25 years with no spike in performance, passed more than 500 drug tests and never failed one." – Armstrong responds in a statement when the US Anti-Doping Agency announces its charges against him.
August 23 2012
"There comes a point in every man's life when he has to say, 'Enough is enough.' For me, that time is now. I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999." – Armstrong announces he won't fight Usada's charges and pursue a hearing to prove his innocence. – AFP