An 18-year-old and a 17-year-old were arrested and taken into custody at a south London police station in the early hours of Thursday morning.
The victim, named as 23-year-old Shane Jerome, was fatally knifed opposite Brixton Tube at 8.20pm on Wednesday, July 21.
Mr Jerome, who lived in Thornton Heath, was said by locals to have been riding a quad bike for a music video outside a chicken restaurant in Brixton market.
Forensics teams have been examining a damaged rental bike and quad bike in the wake of the killing.
Mr Jerome died 45 minutes after being attacked, with paramedics battling to save his life.
A 19-year-old man was also arrested on suspicion of GBH but has since been released with no further action.