Daniel Agger put the Reds into a stunning eighth minute lead when the Dane met Steven Gerrard's reverse free-kick with an audacious backheeled effort that found the net.

However, Rafael Benitez's side were dealt a blow around the half hour mark when Ryan Babel was shown a straight red card following an incident with Benfica defender Luisao.

Holding a numerical advantage, Benfica poured forward in search of an equaliser - but they had to wait until the 60^th minute when Cardozo netted from the spot after Emiliano Insua was deemed to have brought down Pablo Aimar.

And the Eagles striker would again score from 12 yards with 11 minutes remaining after Jamie Carragher was adjudged to have handled inside the box.

But Liverpool head back to Merseyside with what could prove to be a priceless away goal, meaning the tie will be very much in the balance when the two teams cross swords at Anfield next week.

Benitez's charges went into the game on the back of arguably their most impressive showing of the season so far, in which they dismantled Sunderland 3-0 on Sunday.

Indeed, the Reds' team sheet showed just one change to that side as Lucas Leiva replaced the ineligible Maxi Rodriguez, with Rafael Benitez opting to select a starting XI with real attacking intent.

These two giants of the game have enjoyed some memorable tussles over the years, with Kopites able to point to a stunning 4-1 success in Lisbon en route to European Cup glory in 1984, while Benfica's elimination of the Reds from the Champions League in 2006 - less than 12 months on from Istanbul - was still very much fresh in the memory of Eagles fans.

And the Estadio da Luz was certainly the clichéd 'cauldron of noise' by the time referee Jonas Eriksson blew his whistle to get the game underway, although both sides used the opening exchanges as an opportunity to size each other up.

However, the eighth minute brought the opener - and it was Liverpool who claimed the much-vaunted away goal.

Steven Gerrard won a free-kick in an encouraging position on the left edge of the box from Luisao. The skipper took the set piece himself, but while Benfica anticipated an inswinging cross, Gerrard delivered a square pass across the box, which Agger nonchalantly finished with an audacious flick beyond Julio Cesar.

Benfica should have responded almost instantly, but Cardozo somehow contrived to loop the ball over the crossbar from close range after his unmarked run had been picked out by a left-wing centre from Angel Di Maria.

Soon after, the Paraguayan front man rose highest to meet a free-kick inside a crowded box, but his header lacked any power or direction and bounced well wide of Pepe Reina's goal.

Much to the ire of the home faithful, Cardozo spurned an almost identical chance within seconds, this time nodding down tamely from Fabio Coentrao's cross into the arms of Liverpool's goalkeeper.

But Benfica were beginning to dominate, with livewire Di Maria pulling the strings, and it was the diminutive Argentine's cross that presented a chance for Ramires, who headed over from close quarters.

The 22-year-old then took it upon himself to try his luck, fizzing a rising drive towards goal from the edge of the box that cleared Reina's crossbar.

Then, just shy of the half hour mark, Liverpool's plans suffered a blow when Babel was sent off by referee Eriksson.

A reckless challenge by Luisao on Fernando Torres not only resulted in a yellow card for the Brazilian, but it also sparked a mêlée between the two sets of players - with Babel dismissed for raising his hands at the Benfica centre-back.

With an hour still to play, the Reds' task of retaining their lead was going to be an uphill one and only a fine defensive header by Agger brought an end to Di Maria's jinking surge and cross, before the Eagles' No.20 dragged a strike wide seconds later.

Liverpool thought they'd extended their lead on 37 minutes against all odds, though, when Torres fired a half-cleared free-kick into the back of the net from an acute angle - but the raised flag of a linesman brought celebrations to an abrupt halt.

The Spain striker then cannoned an effort into the legs of David Luiz after latching on to Glen Johnson's quickly taken throw into the host's box, while Javi Garcia clipped over at the other end.

In first-half stoppage time, Insua received a booking after hauling back Pablo Aimar meaning he will miss the second leg at Anfield.

The incident also prompted another spate of pressure from Benfica, in which Reina's punched clearance fell for Di Maria. His volley was repelled by the custodian and Liverpool made it into the interval still holding onto their lead.

But Cardozo should have equalised on 49 minutes when he met Di Maria's corner with a towering header that he powered over from six yards out.

However, it was his free-kick that led to a Benfica penalty on 58 minutes, when Aimar was deemed to have been fouled by Insua in a frenzy inside the area after the original set piece had cannoned against the post.

Cardozo took the spot kick himself and was this time able to beat Reina with a powerful low strike.

Liverpool's response saw Gerrard arc a cross centimetres above the head of Torres, who was well placed to pounce inside the six yard box.

The Spain star uncharacteristically spurned a golden chance with less than 15 minutes on the clock, dragging a shot wide when one-on-one with Cesar after being released by Dirk Kuyt following a quick counter-attack.

But the hosts were awarded a second penalty kick three minutes later after Carragher was penalised for handball as he attempted to block Di Maria's cross on the slide. Cardozo was again the beneficiary, netting from 12 yards.

The strike ensured Benfica claimed victory on the night, but Agger's away goal could yet prove priceless when the Portuguese side visit Anfield next week on what promises to be another memorable European occasion in front of the Kop.