It was a two-minute spell from the Petershill side which ultimately ended Rangers’ four-year unbeaten run in the competition, with the contest defined beforehand by a heroic goalline block from Kimberley Smit to deny Wilkinson what looked destined to be the opening goal earlier in the second period.
City struck first from a corner when Forrest bundled over the line from Lisa Evans’ delivery, before Jenna Fife was picking the ball out of her net two minutes later when the forward let fly into the top corner from 25 yards out.
Katie Wilkinson restored a modicum of hope with two minutes remaining in the contest when she fired home, but time ran out on the Gers who will now dust themselves off quickly for the visit of Partick Thistle in league action on Wednesday evening.
Leanne Crichton made just the solitary change to her side from the triumph over the same opposition seven days ago as Jodi McLeary replaced Eilidh Austin in defence.
Such has been the development of 16-year-old May Cruft over the last 12 months that it hardly grabbed the headlines when she was given the nod in the engine room.
She certainly started brightly with a couple of twists and turns in midfield, helping carve out the opening chance for Rangers when Nicola Docherty tempted Calliste Brookshire into space and the Greek international’s cross wasn’t quite turned goalwards by Mia McAulay at the far post.
The Gers looked the more likely of the two sides to break the deadlock in the opening exchanges as a short corner routine saw Brookshire lift a delightful cross to the back stick where Katie Wilkinson peeled into space, but when her header was palmed back into a dangerous area it was Lana Golob who was first to react to clear the ball to safety.
City sparked into life for the first time on 21 minutes when Sofia Maatta hared into space on the right and had the time and space to pick out an orange jersey, although Kim Shin Ji underlined her defensive awareness in shuttling across to the front post to intercept the danger.
Natalia Wrobel then collected a pass inside the Rangers penalty area a minute later after Docherty was robbed down by the nearside corner flag, but her effort was straight down the throat of Jenna Fife.
Crichton was soon lamenting the woodwork when her side stole possession high and, a Brookshire delivery later, Shin Ji timed her run perfectly into the danger area but watched her cushioned volley loop off the crossbar.
It was a cagey contest, in truth, as Fife was able to get her fingertips on a strike from Hayley Lauder seven minutes before the interval after the City defender was picked out in space by Linda Motlhalo just inside the penalty area.
The Petershill side were beginning to build a head of steam as the half-time whistle approached as Evans burst into acres of space on the right-hand side and was able to pick out Emily Whelan 12 yards out, but she was unable to get a proper connection on her strike under pressure from McLeary.
Without threatening Fife’s goal City began the second half with a couple of dangerous moments of their own; Motlhalo slipping clear of McLeary on the right before Evans combined with Maatta but her return pass over slightly overhit.
However, a huge opportunity beckoned for Rangers down the opposite end just eight minutes after the restart.
It was initiated by a supreme Leah Eddie pass to free Brookshire in space down the left who strode forward and lashed towards goal. Her effort was palmed straight into the path of Wilkinson by Gibson, but on the follow-up the English forward could only poke goalwards at full stretch where Kimberley Smit was positioned perfectly to block on the goalline.
Down the opposite end, Rangers played their way into trouble moments later as Wrobel almost took full advantage, drawing a fine save from Fife on her left side before Motlhalo fortunately got her feet mixed up on the rebound.
McAulay, hitherto kept in check, hen flashed just inches wide of Gibson’s goal from distance, before the dangerous Wrobel for City sent a delivery into the penalty area which was whipped goalwards in the 40 mile per hour gusts and almost catching Fife out.
However, the opening goal for Leanne Ross’ side arrived just a minute later as an Evans inswinging corner sailed all the way through a cluster of bodies in the six-yard area and was tapped home at the far post by Forrest.
Just as Rangers were reeling from the concession of the opener City doubled their advantage just two minutes later when Forrest skipped inside Laura Rafferty on the left-hand side and smashed an unstoppable effort beyond Fife and into the top corner.
As the hail stones in Lanarkshire lashed down Wilkinson restored hope when a corner skidded through to the forward at the far post and she lashed a thunderous effort into the roof of the net.
Five minutes of additional time were announced, but amid torrential conditions Rangers couldn't muster a leveller at the death as time eventually ran out in the defence of their trophy.
RANGERS: Fife, McLeary (Austin, 73), Rafferty (Sabajo, 84), Eddie, Docherty, Shin Ji, Cruft, Lafaix (Berry, 69), Brookshire, McAulay (Hay, 73), Wilkinson
Subs not used: Kelly, Pegram, Mengwen, Connolly-Jackson, Boyce
GLASGOW CITY: Gibson, Muir, Lauder (Gray, 81), Golob, Forrest, Wrobel (Anderson, 81), Whelan, Evans, Smit, Motlhalo, Maataa
Subs not used: Clachers, Warrington, Harrison, Earl, Thomas, Tanaka, Brownlie