Dressed in a blue prison outfit, the 65-year-old former American football star and actor -- famously acquitted for the 1994 murder of ex-wife Nicole Brown -- was handcuffed to his chair as he closely followed the proceedings.
He smiled as he entered the Clark County District Court room for the first of five scheduled days of legal arguments, in what lawyers have described as a last-ditch attempt to secure his release from jail.
Simpson, who was convicted in October 2008, is serving nine to 33 years in a Nevada state penitentiary for armed robbery and kidnapping, is to testify on Wednesday, followed on Friday by his former attorney Yale Galanter.
In a 94-page petition, Simpson alleges Galanter knew of his intention to recover personal items which he was ultimately convicted of trying to steal at gunpoint from two memorabilia dealers at the Sands Station hotel.
He also claims that Galanter did not tell him about a plea bargain offer that might have resulted in a substantially shorter period behind bars.
Simpson was convicted in the Las Vegas case 13 years to the day after his acquittal in the murder of Brown and her friend Ronald Goldman, following a sensational "trial of the century" in Los Angeles.
Those who testified Monday included Simpson's daughter Arnelle Simpson, who recalled hearing her father a month before the hotel robbery talking about wanting to see some "personal items" that had been located.
"Personal stuff, family stuff," she said. "Pictures. Footballs. Trophies. Things of that sort."
Eric Brent Bryson, who defended co-accused Clarence Stewart, recalled that prosecutors made a plea offer that would have sent Simpson and Stewart for jail for as little as two years if they both accepted it.
But he said he was unaware whether the offer was conveyed to Simpson.
Stewart's conviction was overturned in 2010 by the Nevada Supreme Court, which ruled he couldn't get a fair trial alongside Simpson. Stewart later accepted a plea deal that gave him three years' probation in lieu of a retrial.
Also testifying Monday was Las Vegas businessman James Barnett, a friend of Simpson, who said the one-time San Francisco 49ers running back was "somewhat intimidated" by Galanter and tended not to question him.
"If Mr. Simpson would ask (Galanter) about some specific point in court, he would say, 'That's not important' or 'Don't worry about it'," said Barnett, who visits Simpson occasionally in prison.
Barnett, an engineer, also testified that audio tape recordings -- a key chunk of evidence in the case -- had been analyzed not by experts, but by Galanter and his 15-year-old son.
Getting real experts to do the job, he said, would have cost $5,000 "or maybe a case of beer in Silicon Valley."