Nottingham Forest stunned one of the world's wealthiest clubs by knocking Manchester City out of the FA Cup with a 3-0 third round win in front of the English Premier League club's own fans.
Southend also shocked one of English football's cash-rich teams in Chelsea by grabbing an injury-time equaliser in a 1-1 draw away to the League's second-placed side. Third-tier Hartlepool lived up to their reputation for creating upsets with a 2-0 win over Premier Leaguers Stoke City in the early match.
Non-league Torquay saw off Championship side Blackpool 1-0 thanks to Matthew Green's 31st minute goal. Forest Green Rovers, another non-league side, came agonisingly close to a giant-killing performance before Championship side Derby County fought back to win 4-3.
Elsewhere FA Cup holders Portsmouth were held to a goalless draw at home to Bristol City. Premier League basement side West Brom could only manage a 1-1 draw with League One Peterborough, while 'Big Four' side Arsenal managed to see off Plymouth 3-1.
The day's all-Premiership clashes saw Hull and Newcastle play out a goalless draw while Sunderland gained revenge for their recent league defeat with a 2-1 win over Bolton.
Middlesbrough were made to sweat by non-league Barrow before winning 2-1 and Fulham defeated Sheffield Wednesday by the same scoreline. Meanwhile Leon Osman scored the only goal of the game as Everton beat Macclesfield 1-0. Life was easier for West Ham, 3-0 winners over Barnsley. Cardiff, last season's losing finalists, beat Reading 2-0.
In a clash between two non-league sides Kettering knocked out Eastwood Town, the lowest ranked team left in the tournament 2-1.
Premier League leaders Liverpool earned a hard-fought 2-0 win at Preston in Saturday's late game while English, European and world champions Manchester United are away to Southampton, second-bottom of the Championship, in a repeat of the 1976 final on Sunday.
Second-tier strugglers Forest, who only appointed Billy Davies as their new manager on Friday, struck twice before half-time to pile the pressure on City boss Mark Hughes, who did the Midlands side the honour of playing a near full-strength side, even though Brazil midfielder Robinho was rested.
Nathan Tyson struck from outside the box in the 38th minute to put Forest, who have slipped down the standings since losing to Tottenham in the 1991 FA Cup final, ahead. And they were 2-0 up when Wales striker Robert Earnshaw scored from inside the six-yard box. Forest's victory was completed 15 minutes from time when Joe Garner seized on a poor City throw-in to lash the ball past Joe Hart.
Southend held out for over half an hour at Stamford Bridge, before falling behind when Salomon Kalou headed in a Frank Lampard corner. However, the third-tier side drew level in the 90th minute as Peter Clarke marked his 27th birthday with a goal.
Forest Green, in the third round for the first time in their 118-year history stunned managerless Derby through Jonathan Smith's 14th minute volley from the edge of the area.
And Derby, who play Manchester United in the semi-finals of the League Cup on Wednesday, found themselves 2-0 down just six minutes when Alex Lawless evaded the Rams defence to beat Roy Carroll at the near post. But Rob Hulse's 40th minute header saw the Rams pull a goal back and on the stroke of half-time they were back on level terms through Martin Albrechtsen.
However, Forest Green were far from finished and regained the lead 18 minutes from time through Paul Stonehouse only for the Rams to draw level a minute later through Paul Green. And in the 87th minute Derby's revival was complete when Steve Davies scored from the penalty spot.
Second-half goals from Michael Nelson and David Foley secured managerless League One Hartlepool's passage into the fourth round. But the attitude of Stoke, in the top-flight relegation zone, was summed up before kick-off when manager Tony Pulis rested seven first-team regulars at Victoria Park.
Championship side Plymouth Argyle did even better at the Emirates, keeping the game scoreless until half-time before early second-half goals from Robin van Persie and a David Gray own-goal gave Arsenal a 2-0 lead. But Argyle were not overawed, Karl Duguid making it 2-1 in the 53rd minute before van Persie's second five minutes from time secured victory.