Pro Evolution Soccer 5 (Winning Eleven 9 in Japan and World Soccer Winning Eleven 9 in the US) was released in October 2005. The improvements are mainly tweaks to the gameplay engine, while online play finally made it to the PlayStation 2 version. The game was perceived as much harder by fans, with a very punishing defense AI making it harder to score. This is wideley regarded as the peak of the PES series.
More information: Pro Evolution Soccer 5 Demo