Torres struck twice as the Reds produced a devastating attacking performance to power past their Portuguese opponents and reach the last four.
Dirk Kuyt and Lucas were also on target on a pulsating night at Anfield as the Reds overturned a 2-1 deficit from the first leg of their quarter-final tie.
Their first-leg nemesis Oscar Cardozo threatened to make life difficult with a goal that made it 3-1 on the night but Torres' second delightful finish ended the contest.
It was a performance that came in marked contrast to Liverpool's struggles in the Premier League and their increasingly forlorn attempts to finish fourth.
They left the field frustrated after being held at Birmingham on Saturday but, after a slow start, their determination to progress in this competition soon became obvious.
They made two changes from the weekend, the key one being the deployment of first-leg goalscorer Daniel Agger in the unfamiliar role of left-back due to Emiliano Insua's suspension.
Jamie Carragher and Sotirios Kyrgiakos started in central defence while Javier Mascherano replaced the ineligible Maxi Rodriguez.
Torres, who was controversially substituted at Birmingham to rest a knee injury, showed worrying signs of discomfort in the early stages.
His mobility was not helped by a crude early challenge from Sidnei and that set the tone for a night of rough treatment for the Spaniard, who had clearly been identified as the dangerman.
Benfica actually started the stronger and had an early opportunity after Carragher pushed the charging Pablo Aimar over on the edge of the box.
Angel di Maria's free-kick went straight into the wall and was put behind for a corner.
Liverpool took time to find their stride and it was not until the 15th minute that they worried Benfica as Steven Gerrard's whipped free-kick was headed behind by Amorim.
Gerrard then fired in a cross for Torres but the striker, who headed straight at Julio Cesar anyway, was offside.
Torres had another chance from a Glen Johnson cross but his glancing header went wide.
The Reds were taking charge and although Benfica continued to look dangerous on the break, they carried the greater threat.
They levelled the tie in the 27th minute after Yossi Benayoun won a corner on the left.
Gerrard delivered a perfect cross for Dirk Kuyt from the resulting set-piece and the Dutchman firmly headed home from six yards.
A moment of confusion followed as the goal initially appeared to have been disallowed as the assistant referee on the far side flagged for offside.
Liverpool protested and the referee and additional assistant behind the goal agreed the goal should stand.
With an away goal in the bank, that gave the Reds the edge overall but they had the momentum and wanted more.
They followed up with a second goal six minutes later as Gerrard slipped the often-maligned Lucas in on goal with a superb ball.
The Brazilian showed great composure to swerve around Cesar and tap in his first goal in 11 months.
The job was far from done, however, and Liverpool survived a couple of scares before the break as Cardozo fired a free-kick at Jose Reina and Sidnei had a shot deflected for a corner.
But Benfica captain Luisao almost handed Liverpool another goal early in the second half.
Kuyt won possession on the right and fed Gerrard, who delivered a low ball across the box.
Luisao slid in to make the interception but lost control and needed Cesar to palm it away.
Liverpool's deserved third arrived just before the hour from a swift counter-attack.
Lucas was struck between the legs as the Reds defended a free-kick inside their own half and left their colleague in pain as they charged downfield.
Benayoun raced into the Benfica half and spread the ball wide for Kuyt, whose first-time cross was swept in by the onrushing Torres.
The atmosphere at this point was raucous, but anxiety soon set in as Benfica pulled one back on 70 minutes after Kuyt fouled Ramires on the edge of the area.
Cardozo, who scored two penalties in the first leg, blasted in a low shot through a gap in the wall.
Benayoun conceded another free-kick in a similar position for tripping the same player four minutes later but this time Cardozo's curling effort flew narrowly wide.
The Reds battled on and showed the resolve to kill off the tie eight minutes from time.
Lucas won the ball in midfield with a powerful challenge and Mascherano sent Torres clear with a brilliant pass.
Torres made no mistake as he raced into the area and clipped the ball over substitute goalkeeper Moreira - a replacement for the injured Cesar just moments earlier - with delicate poise.
Liverpool could at last breathe easily and took off Torres, Gerrard and Benayoun in the closing minutes.