High-flying Everton were knocked out of the FA Cup 1-0 by Third Division Oldham Athletic in the third round on Saturday, becoming one of four Premier League sides to go out to lower league opposition.
Birmingham City, Blackburn Rovers and Bolton Wanderers were the other upset victims, while Havant & Waterlooville carried the minor league flag into Monday's fourth-round draw after snatching a late 1-1 draw at third division leaders Swansea.
Holders Chelsea beat Queens Park Rangers 1-0 at home while last year's runners-up Manchester United went through with a 2-0 success at Aston Villa.
Oldham won thanks to Gary McDonald's 25-metre strike at the end of the first half, with Everton hitting the post in the last minute.
Coventry, 17th in the Championship (second division) and in severe financial trouble, won 4-1 at Blackburn with two goals by Michael Mifsud and one each from Elliott Ward and Dele Adebola.
Havant equaliser
Third Division Huddersfield were also celebrating after a 2-1 home win over Birmingham, while Bolton, having rested Nicolas Anelka and most of the rest of their leading players, lost 1-0 at home to Sheffield United.
An 87th-minute equaliser by Rocky Baptiste earned Havant their replay against a Swansea side who had scored 20 goals in their previous six games.
Southern League Midland Division Chasetown, led Second Division Cardiff City before losing 3-1, while Conference side Cambridge United also led at Wolverhampton Wanderers but lost 2-1 after an 88th-minute goal.
In other all-Premier games Tottenham Hotspur, drew 2-2 with Reading at White Hart Lane, West Ham United and Manchester City drew 0-0 at Upton Park while Wigan Athletic won 3-0 away to Sunderland.