Liverpool manager Rafael Benitez believes Manchester United winger Antonio Valencia dived to win an equalising penalty in his side's 2-1 defeat at Old Trafford.
Striker Fernando Torres gave the visitors the ideal start when he headed in Dirk Kuyt's cross six yards out in the fifth minute.
However, referee Webb's controversially awarded a penalty five minutes later when Valencia went down under Javier Mascherano's challenge despite initial contact being outside the area.
Wayne Rooney converted the rebound after Jose Reina had brilliantly saved his spot-kick but it was not until midway through the second half when Park Ji-sung scored the winner from a diving header.
In the last minute, Torres had a chance to equalise from 10 yards but ballooned his strike into the air and Yossi Benayoun headed tamely into goalkeeper Edwin van der Sar's arms.
"We gave away the penalty too early - but there are doubts about the penalty," said Benitez.
"When you see the replay it is suspicious how he went to the ground."
Asked whether he thought Valencia had dived Benitez said: "From the replay I think so.
"It is not clear but the way he fell down.....is strange.
"It made a big difference. We were playing well and had confidence and then one situation changed everything."
Benitez was involved with a heated touchline exchange with Ferguson after Rooney's goal, with his United counterpart suggesting Mascherano should have been sent off.
However, the Spaniard did not believe Webb had been influenced by Ferguson's comments prior to the game.
"Some decisions in the past have not been the best for us but I consider Howard Webb a good referee," he added.
"The referees are professional. We know the influence of Sir Alex in everything but he is a good referee.
"Jamie Carragher was coming inside so he was in the middle of the action (and therefore Mascherano should not have been red-carded)."
Of their touchline exchange Benitez said: "When you have different opinions you have to express them. He has his own opinion about everything."
Ferguson's opinion differed from that of Benitez.
"I thought it was a red card," he said.
"There was no way Carragher could get across and stop Valencia from shooting - he is too quick for Carragher to get across.
"The law is if you stop someone from having a goalscoring opportunity it is a red card. Not today.
"The referee was right, he tugged him down. He didn't bring him down outside the box; he didn't go down until he was inside the box. The decision was correct."
It was another occasion when Liverpool captain Steven Gerrard failed to perform as, apart from laying on the pass for Kuyt's cross for the goal, he failed to have a significant influence on the game.
There have been a number of games this season when the England international has failed to step up when the side needed him.
The sight of him being shifted from his central attacking midfield role to the left and then the right as Ryan Babel and Benayoun came on did not improve his body language, which has been poor for some time.
Benitez, however, chose to focus on the positives.
"It was a tight game and we had a good chance with Fernando or Yossi late on," he added.
"They (United) didn't create too many chances but they were always dangerous. It was close but the little things make a difference."