The FA Cup has been made famous down the years for so-called "giant killing acts" and this season has proved no different, with non-league team Luton beating Norwich 1-0 and both Liverpool and Tottenham also falling to lowly sides.
Millwall started the weekend of shocks on Friday evening with a fine 2-1 win over Aston Villa at The New Den - a sign of surprises to come.
Leeds United lifted the trophy in 1972 and were revived by the FA Cup spirit to beat Tottenham 2-1.
And, almost as improbably as any of the other feats, League One Oldham Athletic downed a Liverpool team with real ambition in the FA Cup this season 3-2 at a Siberian Boundary Park, inspired by Matt Smith's two goals.
Queens Park Rangers was eliminated by third-tier MK Dons, continuing a theme of shock results this season after fourth-tier Bradford reached the final of the League Cup this week.
Brentford, which is in third place in League One, looked set to join the list after outplaying Chelsea in the first half on a bobbly, sandy pitch at Griffin Park, taking a 1-0 lead into the break with a goal by Marcello Trotta.
Brazil midfielder Oscar levelled in the 55th with a fine individual strike but the holders, who have won the FA Cup in four of the last six seasons, fell behind again when Harry Forrester slotted home a penalty with 17 minutes left.
Torres' goal set up a replay, which will be played on the same weekend as the fifth-round matches on Feb. 16-17 since the next three midweeks are filled with fixtures in the Premier League, international football and the Europa League.
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Manchester United, meanwhile, had few problems in brushing aside Fulham 4-1 at Old Trafford on Saturday.
A Ryan Giggs penalty three minutes in gave the home side before Wayne Rooney doubled their advantage five minutes half-time.
A Javier Hernandez brace put the result beyond doubt, with Aaron Hughes' late goal nothing more than consolation for Martin Jol's side.
Meanwhile, a late goal from Pablo Zabaleta ensured that Manchester City advanced to the fifth round after a 1-0 win over Stoke City.
Right-back Zabaleta emerged as the unlikely hero as the Argentinean went forward with five minutes remaining, diverting the ball home adeptly and putting City through to the next round.
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FA Cup Fourth-Round Results
Millwall 2-1 Aston Villa
Stoke City 0-1 Manchester City
Bolton Wanderers 1-2 Everton
Brighton & Hove Albion 2-3 Arsenal
Derby County 0-3 Blackburn Rovers
Huddersfield Town 1-1 Leicester City
Hull City 0-1 Barnsley
Macclesfield Town 0-1 Wigan Athletic
Middlesbrough 2-1 Aldershot Town
Norwich City 0-1 Luton Town
Queens Park Rangers 2-4 MK Dons
Reading 4-0 Sheffield United
Manchester United 4-1 Fulham
Brentford 2-2 Chelsea
Leeds United 2-1 Tottenham Hotspur
Oldham Athletic 3-2 Liverpool
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