The Scottish Premiership side's victory sees them qualify for their first European final since the UEFA Cup in 2008, which they lost 2-0 to FC Zenit.
Rangers trailed Leipzig 1-0 going into the second leg of the tie, but soon equalised on aggregate through captain James Tavernier, with the skipper scoring from close range in the 18th minute.
The atmosphere was electric inside Ibrox as the home crowd roared their side on to net a second through Glen Kamara, scoring from 20 yards out six minutes later.
Leipzig did pull one back, but it was ultimately to no avail, with Gers' midfielder John Lundstram scoring the Scots' third with ten minutes to go, making it 3-2 on aggregate.
That's when the party stepped up a gear and talkSPORT host Ally was at the centre of it all.
McCoist played more than 581 games for the Scottish giants between 1983 and 1998, later going back to manage them from 2011 to 2014 - earning himself legend status at the club.
And he told talkSPORT how his team's victory shows just how far Rangers have come.
"Incredible, absolutely incredible," he said on Friday's Breakfast show. "I thought I was getting carried away last night, but I'm still getting carried away this morning.
"It was one of those unbelievable nights that European football can produce and you think about it, nine years ago, Rangers were lifting the trophy in the Third Division Championship against Berwick Rangers.
"And then nine years on you're in a European final in Seville against Frankfurt. I'm stunned and so happy for absolutely everybody. The atmosphere last night was ridiculous, it was off the scale."
Giovanni van Bronckhorst's side's victory proved Scottish clubs still have the ability to compete in Europe, despite their inferior budgets to their opponents - and this is something McCoist is particularly chuffed with.
"Where they want to play and where they'll be judged is in Europe, that's why they want to strut their stuff," he explained.
"For Celtic and Rangers to have the opportunity to play at the top level and earn a couple of quid is magic. You think of that budget last night, Rangers spent about £12million on players, it's amazing."
And when asked if he believes Rangers can go all the way in the competition against Frankfurt after Thursday's resounding win, McCoist was as confident as ever, despite thinking Rangers are the underdogs.
"They've got a chance, of course they've got a chance," he said. "I still think Frankfurt will start favourites, which won't bother Rangers.
"I mean Frankfurt are sitting 11th in the league, however, they beat Barcelona at the Nou Camp, West Ham in London so, proper team. But when you manage to hold your own against [Borussia] Dortmund and Leipzig, you're certainly not without a chance.
"I think Frankfurt will start favourites, but I don't think that'll bother Rangers."