Seven-times winners Aston Villa crashed out of the FA Cup at the first hurdle on Saturday when they were beaten 2-1 at home by lower league opponents Sheffield United in the third round.
Both of last season's finalists face replays after holders and Championship side Wigan Athletic were held 3-3 by League One's MK Dons, while runners-up Manchester City survived a torrid test of their class with a 1-1 draw at Blackburn Rovers.
In two of the all-Premier League clashes, West Bromwich Albion were defeated 2-0 by struggling Crystal Palace while Cardiff City, under new manager Ole Gunnar Solskjaer, triumphed 2-1 at Newcastle United to knock out the six-times winners in the Norwegian's first match in charge.
Rochdale, fifth in League Two (fourth tier), made light of the 45 places that separated them from Championship giants and 1972 winners Leeds United by beating them 2-0 to reach the fourth round for the first time since 2003.
Villa's defeat, courtesy of fine goals in each half from Jamie Murphy and Ryan Flynn, who scored with a magnificent 25-metres shot, before substitute Nicklas Helenius responded, heaped more pressure on manager Paul Lambert.
The Scot beforehand had questioned the importance of the competition, describing it as a distraction for the Premier League clubs who enter at the third round stage. He trudged up the tunnel at Villa Park with the wrath of home supporters ringing in his ears.
But it was an day to celebrate for the visitors, ranked 51 places below them in the English soccer pyramid, as they reached the fourth round for the sixth time in seven seasons. "The players were incredible today," manager Nigel Clough told reporters.
"You can fluke a result in a cup, but I thought we deserved that win. We played some magnificent stuff at the start of the second half. "We like to be positive and the lads like to enjoy it, as they did, while working incredibly hard. We've had a rough six months so this puts a smile on people's faces."
Rochdale also had plenty to enjoy after their pulsating display against Leeds. Manager Keith Hill told reporters: "It's tremendous win. We had a gameplan and the players executed it superbly. The players trusted me and each other. No-one can argue we didn't deserve that win.
"Who do I want in the next round? We will see who we get... It is a doubled-edged sword really - do we want a big club to bring in big money or do we want to get through to next round? I'm really not bothered."
Defeated Leeds boss Brian McDermott, speaking to BBC radio, said: "I would probably say that is my worst moment in football." Continuing the joy for visiting managers, Cardiff's Solskjaer was also celebrating having seen his side overturn Papiss Cisse's 62nd minute opener at St James' Park with goals from Craig Noone, from 25 metres, and Fraizer Campbell.
Winners in 1927, Cardiff are famed as the only club to have taken the trophy out of England. In another all Premier League contest, Norwich City drew 1-1 with fellow-strugglers Fulham while Southampton overcame second tier Burnley 4-3 at St Mary's and Everton crushed similarly-ranked Queen's Park Rangers 4-0 at Goodison Park.
Resurgent Crystal Palace struck through Dwight Gayle after 23 minutes, and Marouane Chamakh, in final added time, to maintain their revival under manager Tony Pulis.
Wigan's see-saw thriller with MK Dons was one of the most entertaining ties of the day, Ben Reeves scoring twice for the visitors who came back from trailing 2-0 and 3-1 to secure a replay. Two of the three non-league teams survived, Macclesfield holding three-times winners Sheffield Wednesday, ranked 63 places above them, to a 1-1 draw, and Kidderminster finishing 0-0 against Peterborough, of League One.
Grimsby, however, lost 3-2 at home to Championship side Huddersfield Town, winners in 1922.