The teenager suffered a "long and severe injury, jurors heard.
The killer of a 16-year-old boy twisted a knife into his victim after plunging it into his body, jurors have heard.
Shakilus Townsend from Deptford, south-east London, was beaten with a baseball bat and stabbed repeatedly in a south London in July, the Old Bailey heard.
Doctors said his "severe" injuries were inflicted by twisting the knife.
Danny McLean, 18, and Tyrell Ellis, 19, both from Thornton Heath, and Andre Johnson-Haynes, 18, of Croydon, all from south London, deny murder.
A 16-year-old girl and three youths aged 17 have also pleaded not guilty to the charge.
Shakilus was "lured" in a cul-de-sac by a girl he was smitten with, the court heard.
He was taken to hospital where a team of specialist surgeons battled in vain to save his life.
Dr David Melville said he suffered "extremely heavy" blood loss after one knife wound went through his diaphragm and into his liver, also severing major arteries.
"This was a long and severe injury which had only been achieved by twisting the knife once it had entered through the skin and through the diaphragm," he said in a statement read to an Old Bailey jury.
Doctors were unable to stem the bleeding and the teenager died hours later.
The trial was adjourned until Tuesday.