Touya's four-way game against an arrogant council-man and his posse.
At the same time, Hikaru was learning to do the very same thing, also against four opponents.
Hikaru's game against the Hiroshima best player. Instant hands, and he won. The guy travelling with him (Kawai) thought: "When did he turn into this monster?".
Isumi-san's game against Ochi during the pro exams. Isumi becomes an emotional wreck because of a disastrous game with Hikaru and loses all his matches since then. Ochi, who until then had not lost a single match, dosen't hesitate to gloat and mock him for his losses. Isumi tells him to shut up and proceeds to defeat him without a struggle.
Hikaru also shows his stuff outside of playing matches himself. After watching the Go match between Sai and Kouyou Touya (playing on Sai's behalf), Hikaru actually points out a move after the match over that would've turned the entire match around. And given Touya didn't play it, and Sai's surprise, it's clear neither professional saw that move. Yet Hikaru did. One learning boy spotted a move two professional players missed. Really shows how he's developed as a player.