With United pressing for a winner, goalkeeper Roy Carroll raced out of his area to clear the ball downfield from the left. His clearance was picked up by Pedro Mendes and he coolly lofted the ball right-footed towards the United goal where Carroll was back on his line.
It looked a formality for the Northern Ireland international to take the ball but unbelievably he let it slip through his hands and he was forced to scoop the ball back from a yard inside his net.
But Tottenham looked on in disbelief as both the linesman and referee were unmoved. It was an atrocious decision that left Spurs devastated.
Since the inception of the Premiership, Spurs have only taken one point from 12 games at Old Trafford - but this should surely have been three points for the Londoners.
Until that late controversy, United looked favourites to continue their impressive run, despite their well-documented absentees and the loss of in-form Ryan Giggs with a 37th minute hamstring injury.
The Red Devils had numerous chances to score, but they found Spurs goalkeeper Paul Robinson in outstanding form.
He twice denied Alan Smith with superb reflex saves from point-blank range in the first half.
Robinson continued his England form saving from Cristiano Ronaldo at full stretch, and then racing off his line to deny Giggs' replacement David Bellion.
Spurs did have a stroke of luck when Noe Pamarot tried to cut out Phil Neville's right-wing cross and only succeeded in crashing a ten-yard shot against his own post.
Even after the Mendes 'goal', United went close with a last-gasp effort when Robinson acrobatically threw himself across goal to palm away Gabriel Heinze's viciously curling free-kick from the left edge of the penalty area.