In the second minute the England midfielder's free-kick sailed straight into the Stoke goal but referee Andre Marriner - with a linesman's flag raised - ruled out the effort.

Television replays showed Dirk Kuyt, who followed the ball into the net, was not in an offside position.

Stoke then mounted a magnificent rearguard action to claw their way to a 0-0 draw.

"The disallowed goal was a key decision. If that had been allowed it would have been a much more open game," said Benitez.

"I have no idea why the goal was disallowed. The referee told Jamie Carragher that it had been his decision, not the linesman's.

"But it was a massive mistake. And nobody knows why the effort was ruled out."

Gerrard, who had taken his goals tally for the club to 99 with a double in Marseille in midweek, was engulfed by celebrating colleagues before Liverpool realised the effort had been ruled out.

Benitez said: "The players worked very hard. They tried everything, but maybe we needed a little more ability in the last third to make use of all that possession and all those shots."

Stoke boss Tony Pulis admitted his side had been fortunate to escape "with a decision that went our way at Anfield".

Pulis said: "I was delighted with our performance, my players fought for everything.

"And we had a little luck. We got a decision at Anfield that went our way!

"But I don't know why that early effort was ruled out. It certainly was not for offside, I have been told by people who have seen the replay that Kuyt was not offside.

"Is that what the referee said? Well, I'm not going to argue with us getting some luck here."

Pulis preferred to concentrate on the superb defensive effort his players put in despite being dominated by the hosts throughout.

"I would rather recall what a fantastic performance it was by my team," he added.

"To come to Anfield against a really great team and get a point like that is very pleasing.

"My players fought for everything, they won everything in the air and that is pleasing because the longer it goes at Anfield with you under the cosh, the more chance is that they will finally get one."