Of the many spectacular moments and reactions, the best was Magnus winning a lost position and believing it won him the match (and implying Alireza has much to learn before being able to beat him). Magnus was still a professional when defeated, but emotions were running high at the point in the match.
Also, if you watch the game right after the Magnus victory, Magnus once again declares 'This is just game' before Alireza masterfully turns an amateur position into a victory over the world chess champion.