The 36-year-old son of the Rocky star died of a suspected overdose July 13, and devastated friends and family inluding his father gathered for a private memorial service to pay their respects.
The service, held at St. Martin of Tours Catholic Church, was also attended by Stallone's wife Jennifer Flavin, his longtime friend and attorney Marty Singer, and Sage's mother - Stallone's first wife -- Sasha Czack.
RadarOnline.com previously reported details of the planned service with a source confirming it would be "a celebration of his life."
Sage's famous dad, 66, is overwhelmed at the tragic loss of his son.
"This agonizing loss will be felt for the rest of our lives," he said in a statement. "Sage is our first child and the center of our universe and I'm humbly begging for all to have my son's memory and soul left in peace."
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 Los Angeles apartment where his body was found. Toxicology test results are still pending.