Michael Ballack's late strike put Chelsea into the last eight of the Champions League after they came from behind to beat Porto.
The visitors took the lead when Ricardo Quaresma beat the offside trap to slide the ball under keeper Petr Cech.
The Blues equalised when Porto keeper Heldon let a fairly tame Arjen Robben shot slip through his hands.
And with 10 minutes left Ballack was on hand to volley in Andriy Shevchenko's carefully-weighted headed pass.
For a while it seemed that Jose Mourinho's multi-million pound outfit would bow out at the first knock-out stage.
606: DEBATE
The Blues were poor in the first half, with wayward passing and a resolute Porto rearguard limiting the home side to a couple of chances.
Those chances were wasted by Ballack, who air-kicked Ashley Cole's cross, and Frank Lampard, who failed to connect with Shevchenko's through-ball.
Porto took the lead after just 15 minutes when a slick move ended with Quaresma poking the ball under the body of the outstretched Petr Cech after picking up Lucho Gonzalez's pass.
Thereafter, at least for the rest of the half, the visitors looked in control and it seemed only a mistake or a moment of brilliance would affect their position.
As it happened, it was a mistake. And what a howler it was at the start of the second half.
Robben, who picked up a yellow card for diving early in the half, received the ball on the right and cut inside before firing in a relatively tame shot that keeper Heldon got a hand to, but not a strong enough one as the ball looped into the net.
Chelsea pressed for a winner and sent in a number of teasing crosses testing the Porto shot-stopper, who looked a little jittery after his error.
However, it was not an error that handed Chelsea their much-valued win but a well-worked move that saw Didier Drogba nod Ashley Cole's centre on to the head of Shevchenko who in turn found Ballack.
The German steadied himself, swivelled and fired a low volley from six yards past Heldon and into the quarter finals.
Chelsea will discover on Friday who they are paired with in the last eight.
Chelsea: Cech, Diarra (Ferreira 65), Essien, Carvalho, Ashley Cole, Makelele (Mikel 46), Robben, Ballack, Lampard, Shevchenko (Kalou 84), Drogba.
Subs Not Used: Hilario, Boulahrouz, Bridge, Wright-Phillips.
Booked: Robben, Diarra.
Goals: Robben 48, Ballack 79.
FC Porto: Helton, Fucile, Pepe, Bruno Alves, Cech (Ibson 55), Gonzalez, Ricardo Costa, Paulo Assuncao, Raul Meireles (Adriano 55), Lopez (Bruno Moraes 82), Quaresma.
Subs Not Used: Vitor Baia, Alan, Postiga, Joao Paulo.
Booked: Quaresma, Fucile, Adriano.
Goals: Quaresma 15.
Agg (3-2)
Att: 39,041
Ref: Roberto Rosetti (Italy).