The forward replaced Orlando Berrio with eight minutes to play in Flamengo's 1-1 home Serie A draw against Atletico Mineiro on Sunday morning.
Reports came out earlier in the week suggesting that La Liga giants Real Madrid have already signed Vinicius in a transfer worth close to $67 million, with the young Brazilian set to make the move when he turns 18 in June next year.
Vinicius has starred at youth level for Flamengo and for Brazil's Under-17s where he has scored 19 goals in 22 appearances.
The high-profile youngster's appearance came in Flamengo's first league match of the season, with his future displays likely to be the subject of immense scrutiny.
Vinicius came up against his idol, Brazil international and former Real Madrid player Robinho, asking for his shirt after the full-time whistle.