The Blades almost stun another Premier League side but instead set up a replay.
Watch official Sheffield United v Fulham highlights.
Fulham survived an FA Cup scare against third-tier Sheffield United by battling back to secure a 1-1 draw at a mud-caked Bramall Lane in the fourth round.
Fulham made 11 changes to their starting line-up and League One strugglers United looked set for a repeat of their third-round win over Aston Villa after Chris Porter gave them a 31st-minute lead.
However, the home side had captain Michael Doyle sent off for an off-the-ball incident early in the second period and Hugo Rodallega equalised with 15 minutes remaining to send the tie to a replay.
Heavy rain in northern England made for a muddy, sapping playing surface and the game only went ahead after a late pitch inspection.
There was an early blow for the visitors when John Arne Riise had to go off with an apparent hamstring injury and with half an hour played, United went ahead.
Young centre-back Harry Maguire made an authoritative burst into the Fulham box before driving in a low cross that was stabbed home by the opportunistic Porter.
In reply, Rodallega was denied a penalty after tumbling over a challenge from United goalkeeper George Long, while Pajtim Kasami shot narrowly wide early in the second half.
Doyle was shown a straight red card in the 52nd minute for kicking out at Chris David, but the hosts continued to threaten, with Ryan Flynn working Fulham goalkeeper David Stockdale and Jose Baxter firing wide.
Nigel Clough’s side then had a very strong penalty claim turned down after Flynn was caught by a clumsy challenge from visiting captain Aaron Hughes.
United manager Clough was incensed by referee Andre Marriner’s refusal to award a spot-kick and his mood will have darkened moments later when Rodallega drilled in an equaliser from the edge of the area.
Fulham threatened to complete the comeback with seven minutes remaining, but Philippe Senderos saw his glancing header bounce back off the crossbar.