Harnwell was there when the Glory defeated Parramatta Power in the old National Soccer League Grand Final in 2004 but rates this occasion against the Premier League newcomers on a par.
"There are nerves - but it's not about the result, it's about the performance," Harnwell said.
"I want to go out and perform my best against a team that plays in the best league in the world. It's the biggest game, outside of finals, that I've played for the club.
"If we can put on a good show, hopefully the fans will come back and watch us against Fulham and then North Queensland (tomorrow week) and it will just roll on towards the season," he added.