After featuring prominently during the "Azzurri"'s 2002 FIFA World Cup qualifying campaign, Tommasi was picked by manager Giovanni Trapattoni for the squad that would take part at the finals in Japan and South Korea. He played in all four matches during the tournament, which ended in round-of-16 exit; in the decisive clash against co-hosts South Korea, he came close to scoring twice: first when Roma teammate Francesco Totti played him in only to have his shot blocked by Lee Woon-Jae. During extra time, referee Byron Moreno disallowed him a goal due to a controversial offside decision, and the Italians were eventually defeated by a golden goal.