These are the moments when Chelsea make it seem barely plausible that for long spells this season they appear to have based their entire working operation on the theory of chaos. They played here with character, resolve and togetherness and now have an outstanding chance of reaching the semi-finals of the competition Roman Abramovich craves the most.

It was the kind of night that made their last Champions League excursion, in the bearpit of Napoli's Stadio San Paolo, feel like a trick of the mind.

Here, like then, we had the story of a manager leaving out key names, not afraid to prick a few egos if it meant following his convictions. The difference this time was that there was structure, resilience and not a hint of panic. Napoli had overwhelmed André Villas-Boas side's but Chelsea have already come a long way since Roberto Di Matteo became the latest man to answer to Abramovich.

It culminated in Salomon Kalou turning in a 75th-minute winner after Fernando Torres had manoeuvred space for himself on the right and picked out his team-mate's run into the six-yard area with a perfectly weighted cross.

Benfica had lost only once on their own ground this season but looked ordinary for the most part and Chelsea's belief was embellished as the game reached its closing stages. Had Juan Mata shown a more assured touch when the substitute Daniel Sturridge found him in space they could conceivably have taken a two-goal lead back to Stamford Bridge for the second leg next Wednesday.

Benfica had helped to eliminate Manchester United from the group stages but on this occasion they rarely got behind the visitors' defence. John Terry, whose absence was so crucial in Naples, was exemplary. David Luiz had one of his better nights, applauded on and off the pitch by the supporters of his former club, and Petr Cech made a number of telling saves.

Yet the pressure was sporadic rather than sustained. Towards the end the Italian referee sent Chelsea's goalkeeping coach, Christophe Lollichon, to the stands, but the truth is it was out of keeping with the way the night had gone. Perhaps the most impressive part of Chelsea's performance was the calm they exuded, the sense of assurance and seen-it-all-before knowhow.

Di Matteo's selection was certainly brave and, if they are being truly honest, many Chelsea supporters might also have found it slightly alarming. Frank Lampard, Didier Drogba and Michael Essien had all looked laboured against Spurs on Saturday but it was still a surprise to see them all consigned to the bench, given their big-game experience and how instrumental they had been in retrieving the 3-1 first-leg deficit to Napoli in the last round.

Here, too, was the return of Paulo Ferreira at right-back, playing his first match in almost three months because of the thigh injury that is keeping out Branislav Ivanovic. Ferreira has started only three matches all season and the last one was the 3-1 home defeat by Aston Villa on New Year's Eve. This, however, was a successful return as he quickly set about disproving the theory he could be the weak point in Chelsea's defence.

Ferreira slipped back into the team seamlessly, fully justified his selection ahead of José Bosingwa and was part of the reason Chelsea were relatively comfortable.

Rather than go straight at Chelsea, as Napoli had so devastatingly, Benfica played a more cagey game, making fewer chances. Their best moments in the first half both fell to Oscar Cardozo, first with a left-foot volley that he could not direct on target and then a header that went over. Cardozo did hit the target early in the second half only for David Luiz to clear off the goal-line and Benfica will also reflect on the moment, shortly before Kalou's winner, when Cech kept out Jardel's header.

The Portuguese side had plenty of the ball in telling areas but they seldom made use of it. Chelsea sat back for long periods and, at times, could have taken better care of the ball but, when they did attack, they generally found holes in the home defence. At one point it was something as mundane as a long goal-kick that went straight through the Benfica back four and suddenly Mata was clear, flicking the ball round the goalkeeper, Artur, but taking himself to such an angle that his shot struck the outside of the post.

This was the prelude to Chelsea's best spell of the match and, after they had taken the lead, it was seldom threatened during the final exchanges. Torres had worked hard while still managing to look frustrated and lacking the old sureness of touch. This was the moment, however, he justified his place ahead of Drogba, bursting clear and then picking out Kalou with a deft cross. Kalou had set off with great intent and was still running when he applied the finishing touch.