Hannan became a mainstay on the Sharks' defence corps from the 2000–01 season and evolved as an effective, gritty, shut-down defenceman, earning a selection to the 2001 NHL All-Star Game for the Western Conference in the 2003–04 season. Hannan emerged as a premier defenceman during the 2004 Stanley Cup playoffs, gaining praise for his performance in shutting down star Colorado Avalanche centre Peter Forsberg in the Western Conference Semi-final over Colorado. Hannan played his 500th NHL game at the end of the 2006–07 season in a 4–3 loss to the Avalanche on March 18, 2007.