Mick McCarthy's Ipswich were dumped out of the FA Cup going down to non-league side Lincoln in Tuesday night's third round replay at Sincil Bank.
There were emotional tributes before the match to former Imps manager Graham Taylor, who died last week.
And Lincoln, who had battled to a 2-2 draw at Portman Road, went close in the first half when a header from midfielder Alex Woodyard dropped just wide.
Stand-in Town goalkeeper Dean Gerken then produced a fine save to deny Luke Waterfall at point-blank range.
Just when it looked like the tie was set for extra-time, Lincoln broke from a corner.
Substitute Adam Marriott's pass sent Arnold sprinting clear of a high Ipswich back line and he rounded the goalkeeper before knocking the ball into an empty net - sparking wild celebrations around Sincil Bank, full to the brim with 9,069 spectators.
Championship promotion hopefuls Brighton will be hoping to avoid becoming another scalp when they head to face Lincoln in the fourth round on 28 January.
Fellow non league side Sutton are also in the fourth round after they knocked out 10-man AFC Wimbledon with a 3-1 victory at The Cherry Red Record Stadium to set up a televised tie against Leeds.
Tom Elliott headed the League One side into the lead on 10 minutes, but the Dons defender Paul Robinson was shown a straight red card for pulling back Sutton striker Matt Tubbs.
Sutton were level with 15 minutes left when Roarie Deacon weaved into the area before drilling the ball into the top corner.
Maxime Biamou's last-minute tap-in from close range sparked wild celebrations from the away fans, with Dan Fitchett adding a third from a long goal kick in stoppage time as Sutton secured a televised home tie against the Championship side, winners of the 1972 FA Cup under Don Revie.
Burnley heaped more misery on Premier League strugglers Sunderland with a 2-0 win at Turf Moor.
The Clarets took the lead just before half-time through a header from Wales forward Sam Vokes.
Substitute Andre Gray put the tie beyond Sunderland when he netted a second with seven minutes to go.
Christian Benteke scored twice as Crystal Palace came from behind to beat Bolton 2-1 at Selhurst Park, which secured a date against Manchester City.
League One Bolton took the lead early in the second half when James Henry lashed the ball into the top corner.
Palace got themselves back into the tie after 68 minutes when Benteke headed home, before the Belgian frontman completed the turnaround with 13 minutes left.
Bristol City secured a fourth-round trip to Turf Moor when they knocked out Fleetwood after a 1-0 win at Highbury Stadium.
Jamie Paterson's goal on 17 minutes proved enough to give the Championship side a first victory in nine games and also ended The Cod Army's long unbeaten run at 13 matches.
Blackpool edged their way into the fourth round with a 2-1 over Barnsley, Bright Samuel scoring the winner right at the end of extra-time as the game looked destined for penalties. They will face Blackburn next in the cup.
