Sky Bet League Two side Newport shocked Leicester and managerless Oldham dumped Premier League strugglers Fulham out of the FA Cup on Sunday.
English champions Manchester City brushed aside Rotherham 7-0 and Watford secured a 2-0 win away to Woking, but Championship high-flyers Sheffield United were upset by non-league Barnet.
Padraig Amond's 85th-minute penalty fired Newport into the fourth round as 2-1 winners after Mark Albrighton was guilty of a needless handball in the area.
The penalty came just three minutes after Rachid Ghezzal had levelled for Leicester, who had trailed since Newport's well-worked opener, which was headed in by Jamille Matt from Robbie Willmott's cross after just 10 minutes.
At Craven Cottage, Denis Odoi had put Claudio Ranieri's side ahead in the 52nd minute, calmly finishing after a penalty box scrap.
But they could not add to their lead and Oldham were level with 15 minutes to go after Ryan Sessegnon brought down Peter Clarke and Sam Surridge fired in from the spot, sending Marcus Bettinelli the wrong way.
Fulham had a spot-kick of their own with five minutes to go but Aleksandar Mitrovic saw his shot brilliantly saved by Daniel Iversen, and moments later Callum Lang headed in to give Oldham and caretaker boss Pete Wild a famous win.
— The Emirates FA Cup (@EmiratesFACup) January 6, 2019
Sheffield United may be riding high in the Championship but their FA Cup campaign ended at the first hurdle as Vanarama National League side Barnet won 1-0 at Bramall Lane.
The only goal came from the penalty spot, with Shaq Coulthirst firing in after Ephron Mason-Clark was brought down.
Manchester City had no such problems as they brushed aside Championship side Rotherham.
Pep Guardiola's side had already passed up a couple of great chances before Raheem Sterling's 11th goal of the season came in the 12th minute to put the hosts in front.
Phil Foden's first goal at the Etihad doubled the lead in the 43rd minute and it was 3-0 in first-half stoppage time when Semi Ajayi inadvertently turned in Kyle Walker's cross.
City added to their lead in the second half with Gabriel Jesus tapping in from Sterling's cross and Riyad Mahrez firing in after playing a one-two with Ilkay Gundogan.
Nicolas Otamendi then headed in before Leroy Sane put the icing on the cake.
Woking put up a strong fight against Watford but ultimately went down 2-0 to the Premier League visitors.
Will Hughes' superb 13th-minute strike following a corner gave the Hornets the lead but they struggled to kill off the game.
Javi Gracia turned to Troy Deeney to kill the game off and the captain duly delivered, scoring the second just three minutes after coming on.
Substitute Shane Ferguson scored twice in four minutes late on as Millwall came from behind to beat Hull 2-1.
Jon Toral had put the visitors in front with a fine finish from Nouha Dicko's cross seven minutes into the second half to put Hull in front.
But Ferguson curled in an equaliser in the 82nd minute and then hit the winner three minutes later.
QPR knocked out Leeds with a 2-1 victory at Loftus Road.
Aramide Oteh put the hosts in front from the penalty spot in the 23rd minute after Leif Davis fouled Jake Bidwell, but Aapo Halme levelled moments later when Matt Ingram failed to hold Lewis Baker's free-kick.
Bidwell then headed in the winner with 15 minutes to go from a set-piece.
Doncaster were 2-1 winners at Preston, with Tom Anderson scrambling home the winner in the 72nd minute.
Doncaster had led through John Marquis' early header, but Andrew Hughes levelled 10 minutes into the second half from Paul Gallagher's corner.