Tottenham's grip on fourth place in the Premier League was loosened by a 3-1 loss at Blackpool on Tuesday that enabled the home side to halt a six-match run without a win.
Blackpool captain Charlie Adam, who was close to joining Tottenham last month, netted the opener from the penalty spot.
DJ Campbell and Brett Ormerod scored further goals before Roman Pavlyuchenko's late consolation for Tottenham, which had won its last three league matches and beaten AC Milan in the Champions League last week.
Tottenham remains two points ahead of Chelsea, but the Blues have played a game less.
''We missed about 10 open goals and defended badly,'' Tottenham manager Harry Redknapp said.
Blackpool, which moved five points clear of the relegation zone, soaked up early pressure before the breakthrough came when Sebastien Bassong fouled Campbell as the striker ran across the penalty area.
Adam fired the spot kick beyond diving goalkeeper Heurelho Gomes in the 18th minute.
Tottenham had a chance to level when Pavlyuchenko laid a pass to Steven Pienaar, but the South Africa midfielder's shot was blocked by Craig Cathcart.
Spurs went even closer soon after as Jermain Defoe clipped the ball goalward, but Cathcart was again on hand to avert the danger with a header off the line.
An uncertain moment from Richard Kingson led to Blackpool making another goal-line clearance toward the end of the half, with Alex Baptiste denying Defoe.
''I have never seen a team miss so many open goals in my life,'' Redknapp told the BBC. ''We had chances from two, three, four yards (meters) out and we just couldn't score or hit defenders on the line.''
Campbell doubled Blackpool's lead in the 44th. James Beattie collected Sergei Kornilenko's back heel and chipped the ball to Campbell at the far post, who put it in the net.
Kingson saved a couple of headers from Pavlyuchenko before the third came.
As Matt Phillips broke into the box, Tottenham defender Benoit Assou-Ekotto got muddled as he attempted to make a challenge and the ball broke to Ormerod, who slotted past Gomes in the 80th.
''It was one of the best nights I can remember here,'' Blackpool manager Ian Holloway said. ''Hopefully that will give us a bit of belief, the boys have got great spirit.''
