West Bromwich Albion 1 Tottenham Hotspur 1
The England international striker pounced from the penalty spot after 30 minutes to cancel out Robert Earnshaw's opener for Albion.
Both sides had enough chances to ensure that a replay was not needed, but a combination of the woodwork, good goalkeeping and some poor finishing ensured that the sides will have to meet again at White Hart Lane in two weeks time.
Albion could easily have put the game out of sight before Earnshaw gave them the lead with his eighth goal of the season after 17 minutes.
But the stalemate did at least extend their recent good run to one defeat in the last seven games.
Tottenham ended a sequence of back to back defeats thanks to Defoe's coolly taken spot-kick.
Earnshaw's goal was a just reward for the positive start Albion made to the game.
But Earnshaw really should have struck before the 17th minute as he twice shot weakly at goalkeeper Paul Robinson before hitting the bar from close range.
He rattled the woodwork after a cross from Jonathan Greening, but only had to wait another 60 seconds to make his persistence pay.
Earnshaw nipped in ahead of Anthony Gardner to convert a cross from Ronnie Wallwork with a close-range volley.
The shock of falling behind served to spark Tottenham into life and Defoe capped a spell of pressure to drag the White Hart Lane side back on level terms in the 30th minute.
A spell of Tottenham pressure had seen Fredi Kanoute shoot wide and Simon Davies test Albion goalkeeper Russell Hoult.
When Defoe did strike it was after he had been pulled down in the area by the Albion skipper Darren Purse.
While Purse protested his innocence, referee Mark Halsey had no hesitation in pointing to the spot and Defoe calmly slotted the ball past Hoult.
Defoe then squandered an excellent chance to fire Tottenham ahead - slicing wide in the 49th minute when he only had Hoult to beat from ten yards.
He was fortunate that it was not punished almost immediately as Tottenham successfully rode their luck twice in the space of 20 seconds.
First Greening hit the foot of the post from 20 yards in the 62nd minute before Robinson rescued Tottenham with a superb one-handed save to deny Kanu.
But Tottenham proved equally luckless in front of goal with Davies heading a 67th minute Defoe cross wide from just six yards.
Man of the Match: Jermain Defoe - The pacy England striker proved a constant menace for the Albion defence.