It was the Magpies third consecutive replayed tie and they settled quickly, Gary Jones putting them ahead after 19 minutes. The Blades, who reached the FA Cup semi-finals last season, were slow to get into the game but equalised, against the run of play, five minutes before half-time through a Vassilis Borbokis free-kick.
Twelve minutes into the second half Shaun Murray put County back in front and when Jones' second of the game and sixth in this season's Cup, seven minutes from time, made it 3-1 the Blades seemed out.
But the Sheffield captain, David Holdsworth, pulled a goal back in the 85th minute to set up Marcelo's marvels. His first, with a minute of normal time left, made it three apiece at the end of 90 minutes and the Brazilian grabbed his second four minutes into extra time.
To make things interesting, Wayne Quinn, the Sheffield full-back, was sent off for his second booking - he kicked the ball into the crowd after County were awarded a free kick to set up a nervy finale. "I thought the game was over at 3-1," Steve Bruce, the Sheffield manager, said. "Things like this can only happen in the FA Cup. That's why it is the best competition in the world." "At the moment, football is not a game I'm enjoying," his opposite number, Sam Allardyce, moaned.
The Blades' reward is a fourth-round tie at home to Cardiff City on Wednesday evening.
Was it any real surprise that Second Division Wrexham held First Division Huddersfield Town 1-1 in the fourth round? The Welsh club's pedigree of upsetting their betters in the FA Cup already included wins in the Nineties over Arsenal and West Ham and last season they took Wimbledon to a replay.
The FA Cup's leading goalscorer, Ian Rush, made Wrexham's goal with a sixth-minute pass to Karl Connolly, who beat Nico Vaesen for his fifth Cup goal of the season. The Terriers roused themselves in the 22nd minute when Stuart Croft crossed from the right and Wayne Allison's diving header set up the replay at the McAlpine Stadium.
Bristol Rovers of the Second Division were flattered by their 3-0 win over Third Division Leyton Orient, according to Ian Holloway, the Rovers manager. Jason Roberts, who scored twice in last week's 6-0 demolition of Reading, scored two again. "I knew that if we kept a clean sheet, we had the players to nick one at the other end," Holloway said.
It was knock-out day in Scotland, too, as the Premier clubs emerged from their winter break to hazard humiliation in the Tennents Cup third round.
Certainly Kilmarnock, second in the Premier, still seemed to be in hibernation as they lost 3-0 at First Division Ayr United, their bitter local rivals who knocked them out of the Cup last year, too. Andy Walker scored two penalties in the final 10 minutes. "This one was for the supporters," Gordon Dalziel, the Ayr manager said. "They spent a long time suffering in the shadows of Kilmarnock so it was great for them today."
Struggling Aberdeen, in Paul Hegarty's first game as manager, found no respite in the Cup and were beaten 1-0 at Pittodrie by Livingston, who are top of the Second Division. John Robertson, the former Hearts man, got the all-important goal. "The players must take a close look at themselves as they were well prepared and well warned of what to expect from Livingston," Hegarty said.
The kick-off between First Division Greenock Morton Dundee was delayed by an electrical fault and the lights went out again for the Premier side as Morton won 2-1.
In the day's Nationwide action, Watford lost 2-0 at home to West Bromwich Albion as Denis Smith's side closed in on a First Division play-off place. And Preston North End went to the top of the Second Division after a 1- 0 win at Chesterfield, Ryan Kidd netting.