Mido's first-half header looked to be enough for Tottenham until Ferdinand connected with a Paul Konchesky corner three minutes into stoppage time to turn the ball past Paul Robinson in the Spurs goal.
It was just rewards for Alan Pardew's side who gave a gritty and gutsy performance and pressurised the Spurs goal throughout the final 45 minutes.
The home side came close to breaking the deadlock on six minutes when Edgar Davids' deflected shot off Ferdinand flew just past the post.
And two minutes later Robbie Keane waved his way into the penalty box and saw his shot from the tightest of angles produce a fine save from West Ham keeper Shaka Hislop.
West Ham edged their way into the game and came close on 11 minutes when Marlon Harewood picked out Hayden Mullins on the edge of the box.
Mullins fired a sweet 25-yard drive which had Robinson beaten in the Spurs goal, but the ball flew inches past the post.
But it was Tottenham who broke the deadlock on 17 minutes. Michael Dawson's high ball over the top of the West Ham defence caught out both Ferdinand and Danny Gabbidon.
Mido reacted the quickest and saw his looping header fly over the stranded Hislop and into the back of the net for his fourth goal of the season.
Harewood then had two opportunities to snatch an equaliser for the Hammers. His first came on 20 minutes when his flick header inside the box went just wide of the goal.
And on 23 minutes Teddy Sheringham chested the ball into his path and with the goal at his mercy, he somehow managed to fire the ball wide of the post.
West Ham midfielder Mark Noble could have made a dream opening to his first ever Premiership start for the club.
Sheringham was involved in the heart of the action once again on 40 minutes when he laid the ball into the England Under-19s skipper.
Noble flicked the ball over Robinson into the back of the net, but his effort was ruled out for offside.
Michael Carrick came close to adding a second for Tottenham against his former club on the stroke of half-time when his dipping free-kick went just over the crossbar.
Mido was causing all kinds of problems for the West Ham defence with his aerial threat and came close to adding his second of the game on 52 minutes.
Teemu Tainio's cross into the box picked out the Egyptian forward whose close-range header flicked just wide of the post.
And 60 seconds later Hislop had to be at his very best to deny Keane's acrobatic overhead kick from close range.
Robinson showed once again why he is England's number one keeper when he made one of the saves of the season to deny Sheringham on 67 minutes.
Matthew Etherington's corner eventually fell to the experienced striker inside the box. Sheringham turned on the half-volley and fired a shot which looked destined for the back of the net, but Robinson made a superb one-handed save to push the ball away.
Jermaine Jenas could have secured all three points for Tottenham on 89 minutes, but he saw his curling shot fly just wide of the post.
And they were made to pay when Ferdinand sneaked an equaliser in injury time to earn a well-merited point in a pulsating London derby.