Chelsea's quest for an unprecedented quadruple of trophies remains on track after a sensational late winner from Michael Essien put the English champions into the semi-finals of the Champions League.

Essien, playing his first game since early March because of injury, drove home an angled drive in the 91st minute to put Valencia out in the most dramatic fashion.

Chelsea had looked dead and buried in the first half when Fernando Morientes had given Valencia a 2-1 aggregate lead.

But Andriy Shevchenko levelled and then Essien's last-gasp winner put Chelsea in dreamland.

The enormity of their task in the Mestalla Stadium had been underlined by the inclusion of midfielder Essien.

The Ghanaian international hurt knee ligaments during their 3-3 draw with Tottenham in the FA Cup quarter-final in early March and had not figured for the club since.

But his first contribution of the game was not the one coach Jose Mourinho had anticipated as he was booked for a crude challenge on Morientes.

The Blues were forced to defend in numbers in the 11th minute when Ricardo Carvalho gave away a corner. But Didier Drogba headed David Silva's cross to safety.

The English champions enjoyed large chunks of possession after Valencia's spirited opening but could not force the breakthrough they required.

They were awarded a free-kick when David Albelda fouled Michael Ballack some 30 yards out, but Andriy Shevchenko's effort was blocked easily.

In the 20th minute, John Terry headed a corner by Frank Lampard wide of the target as Chelsea continued to control proceedings.

Another corner found Ballack unmarked but his header went straight into the arms Santiago Canizares.

The Spaniards had been limited to a few counter-attacks and none of those had presented the Blues rearguard with any significant problems.

But all that was to change as Valencia delivered a real hammer blow to Chelsea's hopes of reaching the last four.

It was not as though Mourinho's side had not been warned. Morientes, who had missed the opening leg in London because of a shoulder injury, was clearly determined to set up a semi-final meeting with his former club Liverpool.

He was thwarted from giving the home side the lead in the 31st minute when he smashed a cross from David Silva against Petr Cech's right-hand upright.

But Morientes prevailed a minute later when he escaped his marker to volley home a superbly-delivered right-wing cross from Valencia full-back Luis Miguel.

The goal put Valencia ahead on aggregate but Chelsea could still save themselves by getting on the scoresheet.

However, it was Valencia who almost added a second in the 34th minute when another effort by Morientes was kept out by the legs of Ashley Cole.

It was going to take something special from Chelsea in the second half if they were to preserve their Champions League aspirations.

Mourinho made his first change of the night during the interval when Joe Cole replaced Lassana Diarra with Essien switching to right-back and Chelsea to a 4-3-3 formation.

Cole looked lively as Chelsea attempted to make progress down Valencia's right flank but Lampard was sloppy with his control and the home defence cleared the danger.

There was now greater urgency about Chelsea's play and when Albelda was booked for a foul on Drogba it presented the Blues with the chance to get back into the game.

The booking would rule Albelda out of the semi-final should Valencia win but their chances were handed a setback in the 52nd minute when they failed to deal with Lampard's free-kick and Shevchenko seized on the loose ball to equalise.

Shevchenko's goal put him just three behind Gerd Muller's total of 62 at the top of the European goalscoring charts.

The Ukrainian striker was now spearheading Chelsea's revival but it was his partner Drogba who caused more panic in the Valencia defence when he crossed into the six-yard box.

The home defence partially dealt with the problem but the ball ran loose to Essien who found no power or accuracy in his drive and the chance went begging.

Drogba then wasted a great chance to put Chelsea 2-1 in front on the night when he seized on the loose ball on the edge of the penalty area.

But the player who has smashed 30 goals for the Blues his season saw his effort saved by Canizares who dived low to his right to keep the Ivorian off the score sheet.

Valencia substitute Miguel Angel Angulo wasted a good chance when he shot wide of the target as the Spanish side pressed for the goal that would give them victory.

The Spanish side had Canizares to thank for keeping them in the game in the 84th minute when he produced a sensational one-handed save to keep out a header from Ballack.

But Essien put Chelsea into the semi-finals with a glorious angled drive in the 91st minute.

Teams:

Valencia (1) 1 Chelsea (0) 2

Valencia Canizares, Miguel, Ayala, Moretti, Del Horno,Joaquin, Albelda, Albiol (Hugo Viana 72), Silva,Morientes (Angulo 65), Villa.

Subs Not Used: Butelle, Jorge Lopez, Curro Torres, Nacho Insa,

Pallardo.

Booked: Del Horno, Albelda, Ayala, Moretti.

Goals: Morientes 32.

Chelsea Cech, Diarra (Joe Cole 46), Carvalho, Terry,Ashley Cole, Mikel, Essien, Lampard (Makelele 90), Ballack,Shevchenko (Kalou 90), Drogba.

Subs Not Used: Cudicini, Bridge, Ferreira, Wright-Phillips.

Booked: Essien, Ballack.

Goals: Shevchenko 52, Essien 90.

Agg (2-3)

Att: 53,000

Ref: Kyros Vassaras (Greece).