Michael Jackson's personal physician, Conrad Murray, has gone on trial in Los Angeles, charged with involuntary manslaughter of the singer.
Prosecutors said he acted with "gross negligence" and gave Jackson a lethal dose of the sedative propofol that caused his death in June 2009.
The defence said Jackson gave himself too much of the drug, a sleeping aid.
Dr Murray, 58, who denies the charge, could face four years in jail and the loss of his medical licence.
In Tuesday's opening statement, lead prosecutor David Walgren told the court the evidence would show "Conrad Murray repeatedly acted with gross negligence, repeatedly denied appropriate care to his patient, Michael Jackson".
"That misplaced trust... cost Michael Jackson his life."
The jury was shown a photo of the 50-year-old singer's pale body lying on a stretcher after he died, and heard a recording of the pop star slurring while talking about planned comeback concerts.
Mr Walgren said the audio, aired in public for the first time, had come from a message on Dr Murray's mobile phone.
"When people leave my show, I want them to say: 'I've never seen nothing like this in my life,'" says Jackson, apparently heavily drugged, on the audio.
"Go. Go. I've never seen nothing like this. Go. It's amazing. He's the greatest entertainer in the world."
The prosecutor said Jackson's difficulty in speaking on the recording showed that Dr Murray ought to have realised the star should not have taken any more propofol.
Mr Walgren said that after administering what it says was the fatal dose, Dr Murray had not been attentive to Jackson's health.
The prosecutor said the doctor had left to go to the bathroom and checked his mobile phone.
"He [Murray] left him [Jackson] there, abandoned him to fend for himself," the prosecutor said.
Mr Walgren said when Dr Murray found Jackson unconscious, he did not immediately call the emergency services, instead telling a bodyguard to do so 20 minutes later.
Dr Murray also did not mention to paramedics or emergency room doctors that he had administered propofol, according to the prosecutor.
During his lawyer's turn to speak, Dr Murray appeared to wipe tears from his eyes.
Defence attorney Ed Chernoff said it was drugs taken by Jackson himself which had proved fatal.
"He did an act without his doctor's knowledge, without his doctor's permission, against his orders, he did an act that caused his own death," Mr Chernoff said.
He claimed the singer had swallowed pills of the sedative lorazepam on the morning of his death. That dosage was enough to put six people to sleep, said the defence.
He also said Jackson had given himself a dose of propofol, and that it had killed him instantly.
Mr Chernoff said the two drugs together had created "a perfect storm in his body".
Jackson "died so rapidly, so instantly, he didn't even have time to close his eyes", the defence lawyer added.
He also said that Dr Murray had been trying to wean Jackson off propofol, which the star used to call his "milk".
The prosecutor said Dr Murray had initially asked for $5m (£3.2m) to work with Jackson for a year, though accepted a lower rate of $150,000 per month.
But his contract to become the star's personal physician was never signed, and Dr Murray was never paid.
Jackson choreographer Kenny Ortega was the first prosecution witness to take the stand.
He told the court of Jackson's excitement about his series of comeback concerts.
Mr Ortega also told the court that days before Jackson's death, he expressed "deep concern" in an email to Jackson's concert promoter about the state of Jackson's health.
The email was written after a period of about a week when Jackson repeatedly failed to appear at rehearsals.
But in the last day or two before Jackson's death Mr Ortega said the star seemed "full of energy, full of desire to work... It was a different Michael."
Footage of the star's rehearsals became part of a documentary, This Is It, directed by Mr Ortega.
Paul Gongaware, co-chief executive of concert promoter AEG, followed Mr Ortega to the stand as the second prosecution witness. He told the court about how he employed Dr Murray as Jackson's personal physician.
A number of witnesses, including security guards, paramedics and emergency room doctors, are yet to be called.
Propofol is usually administered intravenously, often during surgery.
Medical experts are expected to testify about the sedative's effects, as well as how a trace of the drug was found in Jackson's stomach.
Hundreds of Jackson fans gathered outside court earlier as the trial began. The trial is expected to last about five weeks.