Manchester City's lead atop the English Premier League was cut to just goal difference after they lost 1-0 to Everton on Tuesday.
Former Manchester United midfielder Darron Gibson scored the game's only goal on the hour mark at Goodison Park.
Gibson's goal would not have only delighted Everton fans, but also those of his former club as they equalled City on points at the top of the league.
After just five minutes, City defender Joleon Lescott was all that stood in the way of Everton taking the lead.
Lescott – who joined City from Everton for a reported fee of 22 million pounds in 2009 – was targeted for plenty of abuse by the home fans throughout the match, but he made a vital intervention to block Denis Stracqualursi's goal-bound header on the line.
Belgian midfielder Marouane Felliani fired wide before City's Samir Nasri produced a superb 25-yard drive that smashed into the bar, with the rebound from Sergio Aguero well-saved by Everton goalkeeper Tim Howard.
The talking point of the first half came five minutes before the interval though, when the match was interrupted after a fan ran onto the pitch and handcuffed himself to a goalpost in apparent protest.
The protester spent five minutes attached to the post before escorted by police.
Everton were resolute at the back and creating enough chances to score, with Gibson opening his account for the Merseyside outfit 15 minutes into the second half.
Royston Drenthe and Landon Donovan were involved in the build-up before Gibson smashed a shot at goal from 25 yards, which hit the back of the net thanks to a slight deflection.
Manchester City boss Roberto Mancini introduced Adam Johnson and Aleksandar Kolarov off the bench as he searched for an equaliser but it was Everton who looked more likely to score, as Gibson saw another long-range attempt go just wide.
City had a penalty appeal when Kolarov's cross was met by Phil Neville but their shouts for handball were turned down.
That was as good as it got for the visitors in the dying stages as Everton held on for a memorable win.