MELBOURNE'S stunning run to a preliminary final was triggered by an upset win over West Coast in Perth – coincidentally the Demons' next opponent on Saturday night.

Key forward Tom McDonald, who booted four goals in Friday night's semi-final triumph over Hawthorn, said the 22-point victory over the Eagles in round 22 was the turning point for the young team's self-belief.

"It's probably just a confidence thing, breaking through that mental barrier and beating a good side. We had beaten good sides, we beat sides like Adelaide, who were top four when we played them and beat them, so we knew we could," McDonald told reporters on Saturday morning. 

"It wasn't like we were that worried about it, it just wasn't quite working. We had wanted it to happen so badly it didn't.

"Once we broke through against West Coast, the mentality of the group was, 'we can win in the hardest stadium in the country to play in, and beat one of the best sides, then why can't we do it against anyone else?' I think it was a mental breakthrough for a few guys."

West Coast has lost only three matches at Optus Stadium this season – to Sydney in round one, a rampaging Essendon in round 14 and Melbourne – and looms as a formidable challenge.

"I'm confident we can do it. It's going to be a bigger ask in finals, they've got (Josh) Kennedy and a couple of their best players back, which is going to make it tougher," McDonald said.

"But I think having played there, seen the stadium and knowing how loud it is – it's deafening over there – we know what environment we're walking into, but that'll give us confidence knowing we can play the ground well."

The last time Melbourne made a preliminary final was 2000, when McDonald's teammate Charlie Spargo was just 10 months old.

"It is a strange feeling, but a few of the boys remarked after the game, by the time we calmed down after five or 10 minutes, it doesn't quite feel as big as it does to other people.

"It just feels like you're playing another game, that it's round 22 or you're on to another one, there's a sense of purpose. More so waking up this morning, it's a pretty cool feeling knowing we've got a chance to (potentially) play in the Grand Final."

With its season on the line, Hawthorn came charging in the final quarter, kicking the first three goals of the term to cut the margin to just 12 points.

But a stunning 50-metre Jake Melksham goal was the steadier the Demons needed.

"I was getting a bit nervous. A few of the Hawthorn players were telling us, 'don't choke now', but luckily we kicked the next couple to shut them up pretty quick," McDonald said.

"You get a bit nervous, but it wasn't panic, it was more we wanted to fix it pretty quickly before it goes too far. We built ourselves a five- or six-goal lead, and knowing they had to kick six goals was a big ask, and if we could just steady it would be alright, and that's what we did."