Striker Amoroso scored twice as South American champions Sao Paulo beat Saudi Arabia's Al Ittihad 3-2 on Wednesday to reach FIFA's Club World Championship final.
Sao Paulo goalkeeper Rogerio Ceni was also on target in a pulsating game in Tokyo the Brazilian club never seriously looked like losing, despite Ittihad's brave resistance.
"Ittihad were very physical and made it difficult for us," said Sao Paulo coach Paulo Autuori. "Amoroso's second was a great goal and in the second half we were the better team."
European champions Liverpool take on Costa Rica's Deportivo Saprissa in Thursday's second semi-final in Yokohama. The final takes place in Yokohama on Sunday.
Ittihad will play the losers of the Liverpool-Saprissa game in Sunday's third-place playoff.
Amoroso gave Sao Paulo the lead in the 16th minute, finding space for a right-foot shot which took a sharp deflection and trickled past goalkeeper Mabrouk Zaid.
Ittihad equalised in the 33rd minute when captain Mohammed Noor bundled in the loose ball after Sao Paulo goalkeeper Rogerio had parried Mohammed Kallon's initial effort.
Amoroso restored Sao Paulo's advantage two minutes into the second half, tucking in Real Madrid-bound Cicinho's low cross from close range after a well-worked move.
Rogerio scored from the penalty spot in the 57th minute to make it 3-1 and give the goalkeeper his 53rd goal since his first-team debut for Sao Paulo in 1993.
Defender Hamad Al Montashari pulled one back for Al Ittihad with a 68th-minute header but the Asian champions never quite had enough firepower to break down Sao Paulo for a third time.
"Our attitude in the first half was wrong," said Autuori. "After we scored we just sat back and lost our shape. The players showed more urgency and application after the break."
Ittihad manager Anghel Iordanescu was left fuming at French referee Alain Sars for waving away two penalty appeals.
"I just wanted to go near him and tell him what a beautiful job he was doing," the Romanian said sarcastically. "I had my own battle with him. If I look tired that's the reason.
"With a little more courage and the same rest period before the match, we could have competed with Sao Paulo. I'm proud of my players. They gave absolutely everything."
Ittihad beat Egypt's Ah Ahly 1-0 at the weekend in the opening match of the six-team tournament while Sao Paulo and Liverpool both received first-round byes.
Japan has proved a happy hunting ground for Sao Paulo, who won the World Club Cup -- the tournament's forerunner, involving the champions of Europe and South America -- in 1992 and 1993.