Man City held in FA Cup, Blades fell Villa
Blackburn Rovers midfielder Jason Lowe (L) clashes with Manchester City striker Alvaro Negredo during their FA Cup third round football match in Blackburn, England on January 4, 2014
Stunned by Wigan Athletic in last year's final, City took the lead at Ewood Park through an Alvaro Negredo goal on the stroke of half-time, only for Scott Dann to equalise early in the second period.
City, currently second in the Premier League, also had defender Dedryck Boyata sent off late on for two bookable offences and now face an unwelcome replay against Gary Bowyer's side.
"I think it was a very close game," City manager Manuel Pellegrini told BT Sport.
"They're a difficult team and they play here with a lot of intensity, so we must decide who continues in the FA Cup at home."
Pellegrini made seven changes to his starting XI, while former England international Paul Robinson returned in goal for Blackburn after spending almost 12 months out due to a blood clot on his lung.
The visitors enjoyed the best of the first half but had to wait until the 45th minute to go ahead, with Negredo volleying home at the back post after Edin Dzeko headed on David Silva's left-wing corner.
City had gone into the game on a run of seven straight wins, but they conceded an equaliser 10 minutes into the second half when Dann pounced after visiting goalkeeper Costel Pantilimon allowed Rudy Gestede's header to bounce off his gloves.
Chris Taylor came close to putting Blackburn in front, while Robinson had to save from Dzeko and substitute Jesus Navas at the other end, before Boyata saw red following an ill-advised swipe at DJ Campbell.
The tie of the round takes place later on Saturday, when Arsenal host north London rivals Tottenham Hotspur.
Aston Villa became the first major casualty of the third round after losing 2-1 at home to third-tier Sheffield United.
Nicklas Helenius appeared to have kept Villa in the competition when he cancelled out Jamie Murphy's deflected opener in the 75th minute, only for Ryan Flynn to give the Blades victory six minutes later.
Former Manchester United striker Ole Gunnar Solskjaer tasted success in his first game as manager of Cardiff City after his new side came from behind to win 2-1 at Newcastle United.
Solskjaer, who succeeded the sacked Malky Mackay on Thursday, saw his new charges fall behind to a 66th-minute Papiss Cisse strike, but two goals in seven minutes from substitutes Craig Noone and Fraizer Campbell gave Cardiff victory.
In the day's two other all-Premier League ties, goals from Dwight Gayle and Marouane Chamakh gave Crystal Palace a 2-0 win at West Bromwich Albion and Fulham drew 1-1 at Norwich City.
Everton crushed Championship high-fliers Queens Park Rangers 4-0, with Nikica Jelavic claiming a brace, while Southampton edged Burnley 4-3 in an entertaining game at St Mary's.
Hull City won 2-0 at Middlesbrough and Stoke City defeated Championship leaders Leicester City 2-1.
Wigan's trophy defence began in uncertain fashion as they were held to a 3-3 draw by third-tier Milton Keynes Dons.
Goals from Roger Espinoza and Jordi Gomez put Wigan 2-0 up, but Ben Reeves struck twice in two minutes to draw MK Dons level and, after Callum McManaman restored the hosts' lead, Patrick Bamford scrambled home a late equaliser.
Bolton Wanderers belatedly exacted revenge for their 4-3 loss to Blackpool in the 1953 final by beating their Championship rivals 2-1, while Leeds United fell to a shock 2-0 defeat at Rochdale.
Meanwhile, the lowest-ranked team in the tournament, non-league Macclesfield Town, claimed a 1-1 draw at home to second-tier Sheffield Wednesday thanks to a 72nd-minute equaliser from Steve Williams.