"The referee made a terrible mistake. You should have technology. The fourth official should be watching the TV monitor and talking to the referee."
Spurs dominated the opening period with goals from Darren Bent and Luka Modric before conceding five second-half goals to lose after the penalty award by Webb, who will referee the FA Cup final between Chelsea and Everton.
The 37-year-old is regarded as one of England's best officials and took charge of two group games at Euro 2008.
So far this season he has issued five red cards, including dismissals for Manchester United pair Cristiano Ronaldo and Nemanja Vidic, in 39 games.
Title is ours to lose now - Rooney
Ronaldo converted the penalty to spark the deluge of goals with the Portuguese forward also scoring a header, Wayne Rooney weighing in with a brace, while Dimitar Berbatov got on the scoresheet to lift the Old Trafford side to the top of the table, three points ahead of Liverpool.
Convinced Gomes had got a hand to the ball before contact was made with Carrick, Redknapp added: "United were not going to win unless something like that happened.
"The referee has not done it on purpose, it is just a bad decision but it was the turning point."
United were denied a penalty by Mike Riley in last week's FA Cup semi-final defeat to Everton when Danny Welbeck appeared to be felled by Phil Jagielka, a decision that United boss Sir Alex Ferguson was quick to highlight in discussing Webb's decision.
"We were a bit fortunate but football is a funny game," said Ferguson.
First goal was key - Phelan
"You get terrible decisions. We got one last week. You have to deal with them and get on with it."
Former Tottenham player Berbatov was impressive throughout, prompting his manager to describe his performance as "fantastic".
"I don't think he gave the ball away once," added Ferguson. "He was our best player in the first-half and in the second he produced some wonderful moments.
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