Union Mills stunned Rushen United to send the cup holders crashing out on Saturday.
The Millers won 4-2 on penalties to shock the home faithful and leave the Croit Lowey side reeling.
The Cu-Plas FA Cup quarter-final tie was level at 2-2 after normal time with Josh Kelly and AJ Suckling both netting twice for their respective sides.
With neither team able to break the deadlock in extra-time, it went to spot-kicks and Mills went onto record a memorable victory.
Old Boys – with 47 year-old former Island goalkeeper John Ward making a surprise appearance – won the tie of the round in convincing fashion.
They won 4-1 at St Mary’s to book their place in the last four.
A hat-trick from Callum Stewart and one from Ian Ramsey ensured Colin Purvis’s side gained revenge from a Railway Cup semi-final defeat to the same opponents.
Marc Priestnal scored the consolation for the below par Saints.
Reigning champions St George’s overcame a potential banana skin by winning 5-1 at Corinthians.
Goals from Ciaran McNulty (two), Frank Jones, Sam Caine and Johnny Myers did the damage with the Geordies 4-1 up at the break.
Chris Cannell had briefly equalised for the home side.
A Second Division side was always guaranteed a place in the last four and Onchan made sure it was them with a 4-2 win at Braddan.
The sides were level at 1-1 at the break but goals from Ally Morris (two), Danny Bentham and Brago Smilyanov booked their place in the draw.
Geoff Murphy and Lee Courier netted for Braddan.