Arsenal hosted table toppers Leicester in the early game and needed a win as they went into the match trailing the Foxes by five points - but it was Claudio Ranieri's side who struck first.
Jamie Vardy won and converted a first-half penalty to leave Arsene Wenger's title hopes hanging by a thread, but Danny Simpson's second-half red card changed everything.
The Leicester right-back was shown two yellow cards in quick succession - to which Ranieri responded by withdrawing Riyad Mahrez - and the Gunners got their reward after throwing everything at the visitors.
Substitute Theo Walcott scored soon after coming on, and fellow sub Danny Welbeck - back after a long-term injury absence - nodded home deep into injury time to earn a 2-1 win and spark wild celebrations.
That left Tottenham and Manchester City with the chance to close the gap at the top in the late game, and Spurs went ahead at the Etihad in controversial circumstances.
Raheem Sterling was harshly adjudged to have handled a point-blank cross, and Harry Kane stepped up to convert the penalty.
Spurs looked to have blown their chance to jump to within two points of Leicester after Kelechi Iheanacho equalised off the bench fot City, but Christian Eriksen struck seven minutes from time to net a 2-1 victory and send Mauricio Pochettino's side back in front of Arsenal.
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