Spurs had looked on course to hand Arsenal their first defeat of the season but were denied by Netherlands international Miedema, who towered above the defence to head home from a corner in the 92nd minute.
The leveller was just reward for Arsenal, who dominated the ball and created a flurry of first-half chances but were denied by the woodwork, with Beth Mead and Katie McCabe coming close.
Miedema should have put Arsenal in front in the 57th minute but missed from close range before Tottenham scored against the run of play eight minutes later through Rachel Williams, who bundled the ball home after Kit Graham’s initial effort.
The hosts had a glorious chance to double their advantage minutes later when Shelina Zadorsky’s shot from a corner fell to Ashleigh Neville, only for the right-back to blast over in front of an open goal.
Arsenal remain top with 19 points from seven games while Spurs are five points behind in third. Second-placed champions Chelsea, who have 15 points, visit Manchester City on Sunday.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies