The 36-year-old son of the "Rocky" star died of a suspected overdose on July 13, and was eulogized at an emotional funeral in Los Angeles on Saturday, reported Radar Online.
The service, held at St Martin of Tours Catholic Church, was also attended by Sylvester's wife Jennifer Flavin, his longtime friend and attorney Marty Singer.
Sage's mother and the Hollywood superstar's first wife, Sasha Czack, also attended.
The 66-year-old actor, dressed in a black suit, a black tie and a white shirt, had his eyes shielded with sunglasses as he was joined by close family and friends for the service.
Following the service, the actor was seen watching his son's casket being taken away by a hearse, which was driven to Westwood Village Memorial Park Cemetery in Los Angeles, where Sage was buried and finally laid to rest.
The star also received support from fans, who were seen holding up placards with pictures of the actor and his son from across the street.
So far no official cause of death has been released for Sage, who was an actor who appeared alongside his dad in "Rocky V", but prescription drugs were found at his apartment where his body was found. Toxicology test results are also still pending.