Just a week after spilling Frank Lampard's routine 35-yard shot, Heurelho Gomes produced another clanger to gift Blackpool the lead with just 15 minutes left.
Moments after saving Charlie Adam's first penalty, the former PSV Eindhoven goalkeeper suffered a rush of blood to the head to barge over Gary Taylor-Fletcher in the box to give the Scot his second opportunity from the spot.
He did not miss, and Spurs seemed destined for only their second home league defeat of the season.
Defoe spared the goalkeeper's blushes as he fired home with under two minutes left, but in reality the draw will mean little if anything to Harry Redknapp, who takes his team to Eastlands on Tuesday with a six-point gap behind Manchester City with three matches left.
Gomes' error will also lead to more questions about his future. The White Hart Lane faithful were quick to heed Redknapp's call to rally round their number one after last week's mistake, but they are likely to not be so forgiving this time. Blackpool fought well for the draw and had chances to claim all three points, but they will be satisfied with the point that edges them out of the relegation zone.
Tottenham, who included Danny Rose in their XI for the first time since he scored a screamer against Arsenal 13 months ago, were made to endure a difficult first half as they failed to convert a number of chances.
Michael Dawson's early deflected 25-yard strike crept just over the bar before Sandro's clinical interception took the ball off DJ Campbell's toes at the other end.
Shouts of "shoot" echoed around the ground as Rose ventured forward on his first surge down the left, but the youngster's goal-bound strike was deflected wide.
Gareth Bale brought the best out of Matthew Gilks moments later with a stinging 25-yard effort before Younes Kaboul just failed to get on the end of a cross while six yards out.
Ian Evatt then threw himself in the way of Defoe's volley after 15 minutes before Luka Modric's deflected 18-yard volley flew a foot wide of Gilks' goal, with the stopper well beaten.
Blackpool, perhaps sensing Spurs' shortcomings in front of goal, grew in confidence.
Gomes pulled off a world-class save to deny Adam from eight yards before Sergey Kornilenko planted a free header over from the same distance.
Spurs hit back on the half hour through Bale, who picked up the ball on the left and drove in a low cross that flashed just past the outstretched legs of Rafael van der Vaart and Defoe.
Defoe had the ball in the net 35 minutes in but he was rightly ruled out for offside after being played in by Van der Vaart.
Redknapp looked to the out-of-favour Aaron Lennon for inspiration as he came on for the ineffective Roman Pavlyuchenko at half time.
The winger made an immediate impact, finding Van der Vaart in the box but he blazed over under pressure.
Bale became the next player to be guilty of failing to test Gilks as he skied a 20-yard strike while in space, but he almost made amends moments later with a screaming low drive that flew inches past Gilks' far post.
Tottenham ploughed on but they were hit by the withdrawal of Bale, who went down clutching his left ankle after being sandwiched by two tackles from Adam and Keith Southern.
The winger was carried off on a stretcher with what looked to be a serious injury just after the hour to be replaced by Peter Crouch.
Gomes pulled off a brilliant save to clip over Campbell's shot before Blackpool earned a penalty when Dawson handled a cross while jumping for a header.
Gomes dove brilliantly to deny Adam from the spot-kick, but the Brazilian soon went from hero to villain as he bundled over Taylor-Fletcher in the box after dropping a Blackpool corner.
Adam beat Gomes to his right this time and celebrated in front of the Blackpool supporters while Gomes was left to reflect on the moment of madness that had cost his team so dearly.
Tensions boiled over as Crouch and Van der Vaart clashed heads after being shrugged off a challenge in the air by opponents and Defoe was accused of elbowing Ian Evatt while jumping for a header moments later.
Spurs pushed for an equaliser and with less than two minutes of time remaining it came through Defoe, who moved into space before firing into Gilks' net.
The England striker came close to winning it with a volley in the sixth minute of injury time but Spurs had to settle for the point which moves them into fifth but means anything but a win at Eastlands will mean they are effectively ruled out of the race for the top four.