Chelsea achieved their mission to reach the Champions League knockout phase by beating Cluj - but it was not without its anxious moments on a night of tension at Stamford Bridge.Luiz Felipe Scolari has presided over a stuttering campaign in the group phase, and so it proved again as Chelsea produced an unimpressive display before finally achieving the victory they required.Salomon Kalou scrambled home Chelsea's opener to break the deadlock six minutes before the interval, only for Cluj to set alarm bells ringing around Stamford Bridge when Yssouf Kone headed an equaliser after 55 minutes.Didier Drogba emerged from the substitutes' bench to steer home the winner with 19 minutes left, but Roma's win against Bordeaux means Chelsea finish second in Group A and face a potentially hazardous last 16 draw.Although they will not meet former boss Jose Mourinho's Inter Milan side until at least the quarter-finals after the Italians could only claim second spot in their group.Scolari insisted he was feeling no pressure, despite failing to secure qualification before the final group game, but Chelsea's nerves betrayed them for long periods before they finally overcame their battling Romanian opponents.Chelsea will need to improve markedly in the knockout phase, but for now Scolari will simply be satisfied to have successfully negotiated his way, albeit unconvincingly, into the latter stages of the tournament.Cluj even threatened a shock in the early exchanges, but were overpowered long before the end.Chelsea, without the suspended Frank Lampard, needed a fast start to ease the nerves inside Stamford Bridge - but it was Cluj who posed the first threat after six minutes when Petr Cech had to push away Alvaro Pereira's shot.Alex had Chelsea's first opportunity, but he wasted a clear chance when he headed off target from Deco's free-kick.Cluj were playing with real freedom in the early stages, and it was only the intervention of Jon Obi Mikel that stopped them from stunning the home support after 16 minutes.Juan Culio's far-post cross was met by Hugo Alcantara, whose header was smuggled to safety by Mikel with Cadu waiting to pounce.Chelsea were starting to move into the ascendancy as the interval approached, with Nicolas Anelka firing just wide and Kalou seeing a shot deflected just over.But just as it looked as if Cluj would survive to the interval unscathed, Chelsea made the priceless breakthrough after 39 minutes.Deco's free-kick caused confusion in the Cluj penalty area, with John Terry heavily involved, and when the ball ran loose to Kalou, he hammered an emphatic finish past Nuno Claro.Chelsea finally found some rhythm in the early stages of the second half, with Joe Cole and Nicolas Anelka both testing keeper Claro.Scolari's side looked to be finally establishing a stranglehold on the game, but Cluj punctured the air of anticipation around Stamford Bridge with an equaliser after 55 minutes.It was a goal of stunning simplicity, with Panin's cross finding Kone at the far post to power a header high past Cech.Chelsea's response was instant and Joe Cole was again denied by a superb save from Claro at point-blank range.Scolari took Cluj's equaliser as the signal to send on Drogba, and he was introduced at the expense of Kalou.And he provided the cutting edge Chelsea required as he restored their lead with 19 minutes remaining.Joe Cole was the provider with a neat pass that Drogba controlled expertly before beating Claro to score only his second goal of an injury-affected season.The goal deflated Cluj and for the first time they appeared resigned to their fate as Chelsea were finally able to exert total control on their resilient opponents.Chelsea saw out the victory in comfort, but the applause that greeted the final whistle smacked more of relief than celebration - a clear sign that they must find another gear if they are to make a real impact on the Champions League this season.Chelsea: Cech, Ashley Cole, Terry, Alex, Bosingwa, Kalou (Drogba 64), Deco, Mikel (Bridge 87), Ballack, Joe Cole (Belletti 74), Anelka. Subs Not Used: Cudicini, Ivanovic, Ferreira, Stoch.Booked: Belletti, Mikel.Goals: Kalou 40, Drogba 71.CFR Cluj-Napoca: Nuno Claro, Pereira, Hugo Alcantara, Cadu, Panin, Muresan, Dani, Culio, Trica (Peralta 72), Dubarbier (Emmanuel Kone 59), Yssouf Kone. Subs Not Used: Hirschfeld, Prette, Deac, De Souza, Ruiz.Booked: Trica, Culio.Goals: Yssouf Kone 55.Att: 41,060Ref: Peter Frojdfeldt (Sweden).