Not surprisingly, Benitez was briefly apoplectic at the prospect of a flagrant disregard of the basic rules of football before sense prevailed and the goal stood.

UEFA have experimented with two extra officials in the Europa League this season, but this was most definitely a case of too many cooks.

There was no debate, however, about Liverpool's second goal seven minutes later, a brilliantly-worked effort that cut straight through the heart of the Benfica defence.

After Mascherano almost lost possession when dallying too long, the ball was fed by the Argentine through Benayoun to Gerrard, whose sliderule pass released the onrushing Lucas to cleverly take the ball around Julio Cesar and tap into the empty net.

Despite the quickfire double, Benfica remained undeterred following a bright opening quarter and Liverpool had a fortunate escape two minutes before the break when, after a Benfica free-kick caused confusion in the penalty area, Lucas cleared Sidnei's low shot against Benayoun and the ball flew wide with Cardozo loitering at the far post.

The home side almost netted in similar fashion shortly after the interval when Luisao's clearance from a Gerrard cross struck a team-mate and solicited a fine save from Julio Cesar.

But the third came on 58 minutes with a classic breakaway goal. After a Benfica corner came to nothing, Johnson released Benayoun to run at pace at the retreating defence. The Israeli's ball wide to Kuyt seemed a touch overhit, but the Dutchman stretched superbly to deliver an inch-perfect low cross for Torres to sidefoot beyond Julio Cesar.

There was another contentious moment on 70 minutes when Kuyt was harshly adjudged to have brought down Ramires, and Cardozo struck a powerful free-kick from 20 yards that deflected off Gerrard and went in to Reina's left.

Benfica now only needed to score once to progress, and moments later Cardozo was almost the beneficiary of another fortunate deflection from a free-kick, the ball this time diverted narrowly wide.

But home nerves were eased eight minutes from time. After a strong challenge by Lucas won possession, Mascherano played the ball over the top for Torres to break the offside trap and chip delightfully over Moreira, who only seconds earlier had replaced the injured Julio Cesar in goal.

In 2001, Liverpool beat Portuguese opposition in quarter-final en route to winning the UEFA Cup. Judging by this performance, they will take some stopping this year – in this competition at least.