Non league Barnet caused the shock of the FA Cup third round after knocking out Championship side Sheffield United 1-0 on Sunday, while Fulham lost 2-1 to League Two Oldham and Leicester were left embarrassed in their 2-1 loss at League Two Newport County.
On another day of surprises following Cardiff, Huddersfield and Ipswich's exits to lower league opposition on Saturday, Barnet beat Sheffield United at Bramall Lane thanks to Shaquile Coulthirst's penalty on 21 minutes.
Sheffield United 0-1 Barnet: Non-league Barnet survive to fourth round
Currently 15th in the National League, Barnet take down Championship side Sheffield United to become the only Non-League club to make it into the FA Cup fourth round.
Sheffield United, third in the Championship and vying for automatic promotion to the Premier League, could not find a way back into the game as Chris Wilder's men suffered a humbling defeat at the hands of the non league side, 15th in the National League.
Leicester, Premier League winners in 2016, suffered as well with Newport claiming an incredible 2-1 win at Rodney Parade. Jamille Matt's header put Newport ahead but Leicester's Rachid Ghezzal equalised eight minutes from time.
A replay looked on the cards but Padraig Amond's penalty in the 85th minute sparked delirious scenes as Claude Puel's men tumbled out.
Fulham 1-2 Oldham Athletic: League 2 side stun Fulham
After Aleksandar Mitrovic missed a penalty in the 81st minute, Callum Lang managed to score the winning goal to secure a place in the fourth round at the expense of Premier League Fulham.
Claudio Ranieri's Fulham reign has got off to a difficult start and it got worse for the former Leicester boss at the hands of Pete Wild's Oldham. Denis Odoi put Fulham 1-0 up after 52 minutes but Oldham hit back through Sam Surridge's penalty before Aleksandar Mitrovic, on as a substitute, had a spot kick of his own saved.
There was still time for further drama as the visitors then took the lead two minutes from time courtesy of Callum Lang.
Elsewhere, League One Doncaster enjoyed a superb 3-1 away win at Championship side Preston. John Marquis gave the visitors a fifth minute lead before Andrew Hughes equalised 10 minutes into the second half but Grant McCann's men stormed into the fourth round thanks to further strikes from Thomas Anderson and Mallik Wilks.
QPR 2-1 Leeds: Historic victory for Queens Park Rangers
QPR get their first FA Cup win without needing a replay in 22 years, downing Championship-leaders Leeds United.
Marcelo Bielsa's much-changed Leeds side once again fell in the third round after a 2-1 defeat away at Queens Park Rangers. Steve McClaren's men went ahead through Aramide Oteh's penalty on 23 minutes but Leeds hit back quickly thanks to Aapo Halme. But McClaren's men made the fourth round thanks to Jake Bidwell's strike 15 minutes from time.
Elsewhere, there was no shock at Woking as Watford eased to a 2-0 win thanks to goals from Will Hughes and Troy Deeney while Shane Ferguson's double helped Millwall to a 2-1 win at home to Hull City.
Manchester City, meanwhile, thrashed Rotherham 7-0 at the Etihad as Pep Guardiola named a strong side following the win over Liverpool on Thursday. There were seven different scorers as Raheem Sterling, Phil Foden, Semi Ajayi's own goal, Gabriel Jesus, Riyad Mahrez, Nicolas Otamendi and Riyad Mahrez all netted in the rout.