Winfrey appeared on "CBS This Morning," telling hosts about the interview she taped with Armstrong on Monday: "We were mesmerized and riveted by some of his answers. I feel that he answered the questions in a way that he was ready. ... He certainly had prepared himself for this moment. ... He brought it. He really did."
The network reported that senior government officials are recommending that the federal government join a whistle-blower lawsuit filed against Armstrong by his former teammate and another Tour de France champion stripped of his title, Southern California's Floyd Landis.
There is a Thursday deadline for the government to join that lawsuit, which claims that Armstrong defrauded his team sponsor, the U.S. Postal Service, by using performance-enhancing drugs and engaging in blood doping to fuel his record seven Tour de France titles.
Until now, Armstrong has been steadfast in his prior denials of cheating, even bullying those who questioned his results.
Winfrey said, "I would say there were a couple of times where he was emotional. But that doesn't describe the intensity at times. ... I would rather people make their own decisions about whether he was contrite or not."
The U.S. Anti-Doping Agency released an October report detailing Armstrong's transgressions, based on statements from 11 former teammates, and banned him from competition for life. He was then stripped of his Tour titles.
CBS reported that Armstrong could be moving to pay back money to the Postal Service and to cooperate with anti-doping authorities by detailing information about others who cheated.
The confessions to Winfrey during a 2 1/2-hour conversation at the Four Seasons Hotel in Austin, Texas -- to air Thursday on the Oprah Winfrey Network -- could leave the 41-year-old athlete subject to paying civil damages and perhaps facing a renewed criminal probe.
Federal prosecutors ended their investigation last February in Los Angeles after calling witnesses before a grand jury. At that time, prosecutors did not elaborate on the decision to end the probe.