The 31-year-old midfielder has impressed with his own form but elsewhere there has been a nervousness after taking the lead in games - Middlesbrough were unfortunate not to earn a point last weekend like Tottenham recently did.

Then Fenerbahce snatched victory from the jaws of defeat in Istanbul last night after Avram Grant's men looked in total control and cruising towards the Champions League semi-finals.

"It's the Champions League and you have to concentrate for the 90 minutes," said Ballack, who famously lost out on three trophies in little over a week with Bayer Leverkusen.

"One second that you don't concentrate, you concede a goal and the game changes.

"It was our fault against Fenerbahce because we controlled the game, had everything in our hands but didn't concentrate for every second. That's our fault. We have another game to put it right.

"It's very disappointing when you have everything in your hands and throw it away. It should not happen but it did and we have to put a line under it."

There is no time to dwell on the trip to Istanbul as Grant's men need victory at Manchester City on Saturday to maintain their Barclays Premier League challenge.

Only Arsenal and Everton have beaten City at Eastlands in the league this season, but anything less than victory for Chelsea will tighten Manchester United's grip on the title.

Fenerbahce then make the trip to Stamford Bridge on Tuesday to defend their 2-1 Champions League quarter-final lead.

"Of course, at home we are very strong," Ballack added.

"It was the same against Olympiacos in the last round. We knew they could score away from home but we played well over 90 minutes and concentrated - and we have to do it again."

Frank Lampard looked angry when he was substituted against the Turkish champions but boss Grant played down the midfielder's reaction.

Of more concern to the Chelsea boss was that Lampard could not play the entire game on his comeback from a stomach virus.

Petr Cech did not make the trip to Turkey and Carlo Cudicini, his deputy, looked nervous at times, although he could do nothing about Deivid's stunning strike that earned a first-leg lead.

Cudicini said: "I don't think we collapsed, it's just sometimes we need to close out games.

"It has sometimes happened this season. When you don't close out the game, the opposition have got a chance if they score."

Cudicini feels Chelsea are still in a good position to progress to the semi-finals, where they would face Arsenal or Liverpool.

"We are confident," he said. "We have shown we have the ability to play very well, as we did in the first half. We know we can beat them at the Bridge."

Striker Didier Drogba agreed, adding: "We created a lot of chances which is good for the second leg, we know we will have a lot of chances but we have to score them."