Albion Rovers caused the shock of the day after a 90th-minute goal from Gary Phillips earned them a 1-0 win over Premiership side Motherwell.
Albion, second from bottom of the fourth tier of Scottish football, switched the tie to Hamilton's New Douglas Park where a crowd 2,950, mainly made up of the 'away' fans, were stunned with just seconds remaining.
Albion keeper Neil Parry had kept his side in the game with a fine save from Well striker John Sutton before Phillips sent the Coatbridge side into Monday's fifth-round draw with a left-foot shot that gave Gunnar Nielsen no chance.
And they will be joined in the Hampden draw by Stenhousemuir who saw off non-league Fraserburgh 3-0 thanks to two goals from Ross McNeil and a 90th-minute clincher from Errol Douglas.
Alloa recovered from the loss of an early goal to edge a five-goal thriller with Stirling Albion.
Jordan White's ninth goal of the season put the visitors ahead but Ryan McCord (51) levelled before Graeme Holmes (59) put Athletic 2-1 up.
Jason Marr's 90th-minute goal meant no way back for the visitors who grabbed a consolation with almost the last touch of the ball through Graham Weir.
Martyn Fotheringham scored in the 90th-minute to earn Forfar at 1-1 draw at Brechin, who had taken the lead in the 53rd minute thanks to Alan Trouten's seventh goal of the season.
Brechin finished the game with 10 men after Ewen Moyes saw red towards the end of the first half, but that was one more than the visitors who lost the services of Stuart Malcolm in the opening 15 minutes and Mark Baxter late on.
An eighth-minute own-goal from Gary Irvine was enough to earn Raith Rovers a 1-0 victory at fellow-Championship side Dundee while Stranraer earned a replay after Jamie Longworth (44) cancelled out Kieran MacDonald's 15th-minute opener for Clyde.
But one of the stories of the day was provided by Stranraer captain Frank McKeown, who played despite having worked at the scene of the horrific helicopter crash in Glasgow overnight.
McKeown was on duty until 8am in his role as a rescue fireman before heading to Clyde to lead his side out in a truly inspirational tale.
Dumbarton hit back from the loss of an early goal to beat Berwick Rangers 3-1 at Shielfield Park.
Lee Currie fired the home side in front with an eighth-minute free-kick but Bryan Prunty levelled from the spot on the half-hour mark after Stephen Tulloch had handled in the box.
Mitchell Megginson capped off a spell of Sons pressure with a second two minutes from the interval and Scott Linton ended the scoring for the visitors 10 minutes into the second half.
Ayr United and Dunfermline must reconvene at East End Park early next month after a thrilling 1-1 draw at Somerset Park.
The Pars survived an early home onslaught before taking the lead against the run of play through Andy Geggan in the 14th minute.
But after repelling a spell of pressure from the visitors, Ayr deservedly levelled when Michael Donald pounced on the hour mark.