José Mourinho was forced into an embarrassing climbdown last night after launching a strong attack on Markus Merk’s failure to award Chelsea a penalty in their 1-0 win over Liverpool. Chelsea have put themselves in control of the Champions League semi-final courtesy of Joe Cole’s first-half goal, but Mourinho was more concerned by the German referee’s decision to ignore a handball by Álvaro Arbeloa at the start of the second half.

The Spanish defender handled the ball under pressure from Frank Lampard, though television replays clearly showed that contact was made some distance outside the penalty area. The Chelsea manager was not interested in a second viewing, however, launching a strongly worded outburst in a television interview that echoed last weekend’s complaints about “the new rules of football” being against Chelsea.

“I don’t understand why we don’t get penalties,” Mourinho said. “When the penalty is so clear I don’t understand. I just speak about facts and it’s a fact. It’s happening and happening and happening. A penalty is a good chance for 2-0 and 2-0 is a different story. I hope after the second leg we’re not crying again over a big decision.”

Having been told of his error, Mourinho was forced to admit that there was some doubt about the incident, though he was still critical of Merk and hinted at a deeper conspiracy. “First of all it’s a handball, that’s no doubt,” he said. “But if it’s inside the box and a penalty or outside the box and a free kick, I don’t know.

“For me the referee was top, but he made a mistake with the handball. It was a big mistake, but if it’s a free kick it reduces the possibility of us scoring. He made a mistake, but normally the mistakes are against Chelsea.” Rafael Benítez’s sarcastic response reflected the animosity between the pair.

“I’ve not seen a replay, but if he says it’s a penalty, I’m sure it’s a penalty,” the Liverpool manager said.

Mourinho’s complaints left a sour note at the end of an evening that he should have savoured. The Portuguese will take his players to Anfield for Tuesday’s second leg knowing that avoiding defeat will secure the club’s first appearance in a Champions League final — Manchester United or AC Milan await the winners — with confidence high as a result of a 22-match unbeaten run since their last visit in January.

“I’m more than happy with the players, the performance was top,” Mourinho said. “The first-half performance was superb and we had five or six chances to score. We should have scored more, but we’re 1-0 ahead, which is a positive result, and Liverpool have to beat us.

“They play at home and have the historical advantage of success in the Champions League over decades. On Saturday Liverpool will play Portsmouth and it’s not important for them, but we have a cup final against Bolton.”

Benítez admitted that his side had underperformed but he has not given up hope of reaching a second final in three years. “I’m disappointed because in the first half we did not play well and were giving the ball away too easily,” he said. “At this moment, playing at Anfield will be good for us. We won 2-0 [against Chelsea] in January, which is a good message to my players.”