LOS ANGELES (CNN) -- He was combative, tearful, funny and masterful. He even drew a warning from the judge that he wasn't supposed to act like a lawyer trying to take over the trial.
Many observers are wondering whether and to what degree Donald Sterling is mentally incapacitated.
The 80-year-old billionaire and co-owner of the NBA's Los Angeles Clippers, took the witness stand for the first time this week in a non-jury trial in probate court. He is battling his estranged wife over how she had him declared mentally unfit and then took over the couple's trust that owns the basketball team, which she's trying to sell for a record $2 billion.
Sterling's testimony, which began Tuesday, is scheduled to continue Wednesday afternoon in a Los Angeles courtroom.
After his first day of testimony -- in which he tearfully asserted his wife, though beautiful and intelligent, just can't run their business empire -- the answer to whether Sterling is mentally incapacitated depended on which attorney was talking.
"The claim that he lacks competency is a sham. It's absurd," said Bobby Samini, Donald Sterling's attorney. "I think Donald did an excellent job on the stand. Of all the lawyers in the room, if I needed a lawyer, I'd hire him."
But the attorney for the man who wants to buy the Clippers from Shelly Sterling disagrees.
"Donald Sterling did nothing but prove the doctors were absolutely correct in their conclusions. You can't help but feel a little sad, sympathy for the man clearly not working with all of his faculties," said Adam Streisand, the attorney for former Microsoft CEO Steve Ballmer.
Donald and Shelly Sterling have been ordered by the NBA to sell the basketball franchise after Donald Sterling was heard making racial slurs against African-Americans in an audio recording.
She took over the trust in which the couple equally own the Clippers after she sent him to two physicians who certified he was mentally incapacitated.
Donald Sterling, an attorney and real estate investor, has early Alzheimer's or another brain disease, the doctors say.
But Donald Sterling and his attorneys dispute he's incapacitated.
Judge Michael Levanas is hearing evidence on whether Shelly Sterling acted properly when she removed her husband from the couple's trust.
The judge said he is not deciding on Donald Sterling's mental capacity. Rather, the judge is going to rule only on issues of the trust and whether its procedures were followed correctly.
Tuesday's court activities had its share of drama.
After Donald Sterling was ushered through the courthouse through a private entrance, Shelly Sterling approached her husband in the courtroom, and he gave her a kiss. She cried and then left the room. She later returned to the courtroom.
When her husband took the stand, it was his turn to become tearful -- when he spoke of how he felt for his wife.
"I trusted my life. I relied on her. I love her," Donald Sterling testified.
He took a deep breath and suppressed a cry.
He pointed out, however, that he never authorized his wife to carry out a sale of their team.
"I authorized her to negotiate," he testified. "Negotiate is not to consummate a sale."
In a contentious exchange while being questioned by his wife's attorney, Sterling said he was negotiating possibly a better deal for the team -- by trying to sell broadcasting rights for Clippers game to the Fox network.
In fact, Donald Sterling believes the team may be worth twice the $2 billion price that his wife has negotiated with Ballmer, said Maxwell Blecher, another attorney for Donald Sterling.
While on the witness stand Tuesday, Sterling cited how another NBA franchise in Los Angeles -- the Lakers -- struck a deal with Time Warner Cable to broadcast its games for 20 years for a reported $3 billion in 2011.
"The reason is that the Lakers signed a deal with Warners for $3 billion. The reason is, I am negotiating with Fox," Sterling said.
At one point Tuesday, Donald Sterling directly confronted his wife's attorney Bert Fields -- known for his fierce litigation in Hollywood's power circles -- who was questioning him.
"Be a man for God's sakes. Stand up and be a man," Donald Sterling said on the witness stand.
But Donald Sterling acknowledged how he couldn't remember dates and times of recent events -- including what he told CNN's Anderson Cooper in May.
By Michael Martinez
CNN's Sara Sidner and Linda Hall contributed to this report.