Real Betis 1 Chelsea 0: Jose Mourinho denied his team were beaten by Charlton a week ago, because they went out of the League Cup only on penalties, but the Chelsea manager cannot claim they did not lose last night. A poor display meant an awful run of away European form continued against a physical, sometimes cynical Real Betis, who hustled their opponents out of a rhythm in this atmospheric stadium.

Chelsea spent almost the entire second half on the attack in search of an equaliser and were unfortunate not to score with their only chance in the 71st minute. A Damien Duff cross just eluded Didier Drogba, who had earlier had missiles thrown at him, and Michael Essien saw a shot hit both posts and end in the goalkeeper's arms after Shaun Wright-Phillips returned the ball.

Chelsea's frustrations showed as their play lacked its normal calm and incisiveness and they ended with John Terry in attack. They will argue that Betis went down too easily for free-kicks and they may now need to win their remaining games in Anderlecht and at home to Liverpool to go through.

Whether Arsène Wenger was watching on the television or through a telescope he will have been encouraged.

Chelsea had known that a victory would take them into the last 16 but their recent results away in Europe had hardly suggested that would be easily achieved. Mourinho's previous five Champions League ties outside Stamford Bridge had produced four defeats and a goalless draw at Anfield.

The manager had castigated his players on the eve of this match for too many defensive errors last month and must have been dismayed when a disappointing run of one clean sheet in six games extended to one in seven before half an hour had been played, leaving Chelsea trailing.

Chelsea had looked solid to begin with in the face of pressure from a Betis team who needed to win to stand a realistic chance of progressing.

The back four looked alert, with Ricardo Carvalho starting positively, and were being aided by Frank Lampard, Essien and Claude Makelele.

Betis had not made a chance of note before they went ahead and Chelsea may have felt that home morale would have dropped when the Spanish team lost two players to injury in five minutes, including their Brazilian forward Ricardo Oliveira, adding to a wretched run of recent casualties.

Yet Oliveira's replacement, Dani, quickly scored. Betis worked the ball across the pitch and to their left and Jesus Capi's cross was not dealt with.

Chelsea were flummoxed by an Edu dummy and William Gallas could not prevent the lively Dani from slamming a shot past Petr Cech from close range.

If that was disappointing for Chelsea, so had been their lack of threat going forward.

They had not carved out a chance before going behind, with Joe Cole and Arjen Robben having little impact on the flanks and the team perhaps struggling to adjust to being without the aerial outlet of Drogba.

The Ivorian had been unexpectedly left on the bench, with the smaller Eidur Gudjohnsen given a rare opportunity to lead the line. Chelsea's early use of possession was looser than usual and though they began to find better range, with Lampard showing good vision at times, their fluency in the first half was not at the level of which they are capable.

Dani's goal at least stung them into a response and with better finishing they could have found the net four times in the space of quarter of an hour before half-time. Cole, Robben and Gudjohnsen became more of an influence and, from a Cole cross, Essien put a free header over the bar.

Cole ought to have equalised when spotted on the right of the area by Gudjohnsen but seemed to think he was offside, delayed a fraction and had his shot saved by Pedro Contreras. The goalkeeper then saved from Robben before Gudjohnsen wasted Chelsea's best opening. Racing on to a long Terry pass, he had just Contreras to beat but shot woefully over.

There remained a threat from Betis, though. Mourinho had warned his player to take nothing for granted despite a 4-0 home win over this team and Cech was twice stretched before the interval. When he fisted out a swerving Edu shot, it was fortunate for Chelsea that Dani put the rebound wide.

The start of the second half showed how unhappy Mourinho had been with his team's performance. Shaun Wright-Phillips and Drogba came on for Cole and Gudjohnsen, and there was a greater intensity about the team's play. Yet Betis were making life hard, closing down fast and Chelsea could find little rhythm or make chances.

They were doing almost all the attacking but Betis posed danger on the break and it was hard to believe they had lost their past four domestic and European games. In search of a breakthrough Mourinho sent on Duff for Robben, with Chelsea facing a second defeat in less than a week.

REAL BETIS: Contreras, Varela, Juanito, Nano (Castellini 20), Melli, Joaquin, Rivera, Arzu, Edu, Capi (Fernando 84), Oliveira (Dani 25). Subs not used: Doblas, Xisco, Juanlu, Israel. Booked: Capi, Varela, Melli, Contreras, Dani. Goal: Dani 28.

CHELSEA: Cech, Paulo Ferreira, Ricardo Carvalho, Terry, Gallas, Essien, Makelele, Lampard, Joe Cole (Wright-Phillips 46), Gudjohnsen (Drogba 46), Robben (Duff 65). Subs not used: Cudicini, Geremi, Bridge, Huth. Booked: Joe Cole, Robben, Drogba, Wright-Phillips, Duff.

Referee: Alain Hamer (Luxembourg).