Officers were called at 5.50pm on Friday to reports of a youth found with stab wounds in Adelaide Close on the Moorlands Estate.
He was en route to hospital when he died in the ambulance 50 minutes later.
While police have not named the victim he has been identified locally as Kwame Asare.
A post-mortem examination will take place on Sunday.
Police believe the victim was with a friend when they were chased by two young men and assaulted.
The victim’s friend was not injured.
The suspects were described as two young black men.
Detective Chief Inspector John McFarlane, leading the investigation, said: “We appeal for anyone with information about this murder to come forward as soon as possible.
“Were you in or around the Moorlands Estate, Brixton on Friday afternoon or evening? Did you see or hear anything suspicious? Do you know who may have been involved?
“We are working closely with our borough colleagues to investigate the death by speaking to witnesses, examining CCTV cameras and conducting forensic examinations of the scene. Our enquiries continue.”
Police are also investigating another incident earlier on Friday in nearby West Norwood where a 17-year-old boy was stabbed.
Officers were called around 1.15pm to reports of a stabbing outside West Norwood bus garage in Ernest Avenue.
The victim was taken to a south London hospital, where he is in a stable condition with serious injuries.
A youth in his late teens has been arrested and remains in custody.
Officers are working to see whether or not the two incidents are linked.
Commander David Zinzan, in overall charge of policing in south-east London, said: “Following the fatal stabbing of a 17-year-old boy in Brixton and the wounding of another 17-year-old boy in West Norwood on Friday, and other serious stabbings in Lambeth borough in the last few days, police have increased patrols in and around the borough.
“Extra officers have been drafted in to reassure and protect the public, and to act as a strong deterrent to anyone thinking of committing further violence in the aftermath of these incidents.”
He added: “Officers are investigating these two cases and are keeping an open mind over whether they are linked at this stage.
“We know the community support us in our efforts to solve crimes of this nature for the sake of victims, their friends and families, and for the community as a whole.
“Plans are in place across south London to prevent and deter further violence and other crime.”
Anyone with information about the murder should call the incident room on 020 8721 4205 or to remain anonymous call Crimestoppers on 0800 555 111.
No arrests have been made in connection with the murder at this stage.
Extra officers are working in and around Lambeth and a Section 60 stop and search power is in place across the borough for at least 24 hours.
http://www.london24.com/news/crime/...d_to_death_in_second_lambeth_attack_1_1227006