Second-half substitute Rascas scored a header nine minutes from time to give Angola a 2-1 victory over Japan on Thursday in Group D at the FIFA World Youth Championship.
Japan looked far more potent in attack than in the opening game against Australia but once again defensive errors proved its undoing and a second successive qualifying-round defeat leaves the 1999 runnerup with only an outside chance of progressing to the knockout stages.
Consadole Sapporo midfielder Koji Yamase equalized in the 61st minute to cancel out an early strike by Mendonca after nine minutes before Rascas pounced to seal the game for the African Champions at the Club Atletico Stadium.
"We were good going forward, but we slipped up at vital moments," Japan coach Akihiro Nishimura said.