The inaugural winners of the competition in 2011, Williamstown will now face off against reigning WAFL premiers West Perth for the 2014 Foxtel Cup title on Tuesday, July 22.
The champions will receive $100,000 in prizemoney while the runners up take home $40,000.
It was a drama-filled build-up for the Seagulls, who endured four flight delays in the space of 18 hours before they finally arrived in Perth on Tuesday.
That included a plane being forced to turn back to Melbourne half an hour into the flight late on Monday night – which also resulted in the side’s luggage being lost.
They only landed in Perth about four hours before the first bounce.
Coach Andy Collins, who led West Adelaide to last year’s Foxtel Cup title, was proud of his players' efforts to run out the match after a less than an ideal preparation.
It is Williamstown’s 150th anniversary this season and they sit inside the top four on the VFL ladder.
“It’s going to be a great story and one that will be in the history of our footy club going forward,” Collins said of the pre-game flight dramas.
“Really an outstanding effort by our boys to persevere.
“We had so many goals going into this year and winning the Foxtel Cup is one of those and to have a chance at a Grand Final is an outstanding effort for the boys.”
Kane Lambert was brilliant for Williamstown, finishing with a game-high 26 disposals and kicking one of the Seagulls four last-quarter goals.
He was well supported by Adam Marcon (19 disposals), Michael Gibbons (15 touches) and Jack Johnstone (15 possessions, six clearances).
Forward Jake Owen also looked dangerous and kicked two goals to be Williamstown’s only multiple goalscorer.
After an even opening term, where the half-back lines of both sides controlled the play, it was the Royals that made the first move.
East Perth, who had seven West Coast-listed players in their line-up, kicked four unanswered goals to lead by 16 points early in the second term.
Among those were two clever goals from lively West Coast Eagle forward Josh Hill – including a right foot snap from near the boundary.
But that sparked Williamstown into action and the Seagulls responded with the next three goals to take a narrow lead into half-time.
The lead swapped four times in the third term with the highlight of the quarter being a brilliant running goal to Williamstown’s Jack Dorgan after four bounces.
Both sides missed relatively easy chances in the final term until Williamstown's Anton Woods bounced home a long goal from 50m late in the match to seal the result.
Another Eagles-listed player, Brant Colledge, led the way for East Perth along with Brendan Lee. They each had 17 disposals while big man Paul Johnson was a presence all over the ground.
Former Richmond and West Coast utility Jarrod Oakley-Nicholls was creative out of defence for East Perth.
Hill finished the leading goalscorer on the ground with three as West Coast coach Adam Simpson watched on.