Chelsea escaped a distinctly uncomfortable night in Transylvania with a goaless draw - but harbouring fresh concerns over the fitness of Didier Drogba.
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Jose Bosingwa is tackled by CFR Cluj's Uruguayan Alvaro Pereira
The Ivory Coast striker was carried off on a stretcher with an apparent knee injury early in the second half.
Despite Frank Lampard's best efforts, Chelsea could not break down the resilient CFR Cluj rearguard - and the battling Romanian double winners were good value for their draw.
Cluj are enjoying a dream debut season in the Champions League, having opened their campaign with a 2-1 win over Roma a fortnight ago, and they now sit level with Chelsea on top of Group A.
The stands shook as the Transylvanian locals greeted the teams by stamping their feet and unfurling a giant image of striker Juan Culio, who scored both goals in Rome, dressed as Dracula and tying a Cluj scarf around Big Ben.
Goalkeeper Petr Cech was called into action in the opening minute to beat Cluj midfielder Sebastian Dubarbier to a dangerous through ball.
Salomon Kalou scuffed Chelsea's first shot on goal, but it came from a promising build-up as Lampard linked neatly with Drogba on the edge of the Cluj box.
John Terry and Mikel John Obi made a hash of clearing a long punt forward but were let off the hook when Yssof Kone tried to lob Cech from 30 yards and floated his effort harmlessly over the bar.
It was a sign of things to come in the first half as Mikel struggled to dominate a limited Cluj central midfield, and Chelsea carelessly conceded possession.
When Florent Malouda did just that, Cluj raced forward - and Chelsea appeared vulnerable only for Culio to pick out Dubarbier in an off-side position.
Lampard was trying to conjure something up for Chelsea. Jose Bosingwa was a regular target down the right flank, but Cluj covered him well.
The Romanians then stepped up the intensity, forcing Chelsea on to the back foot as Alvaro Pereira repeatedly surged forward from left-back.
Periera slipped a pass to Kone, who lofted his cross over Terry's head and towards Eugen Trica. The midfielder attempted a spectacular volley but managed little more than an air shot.
Pereira then launched another incisive Cluj attack, halted only by Bosingwa's vital last-ditch tackle on the Uruguayan inside the Chelsea box.
Pereira charged forward again to meet Trica's lay-off, but his low drive flashed across Cech's goal and just wide.
Nicolas Anelka was sent on in place of Kalou at half-time as Chelsea switched to two up front and immediately looked more dangerous.
Bosingwa almost picked out Drogba, and Anelka then clipped a short ball towards Lampard at the near post - which the England midfielder could not quite squeeze home.
But Chelsea's change in formation did not last long. Drogba threw himself at a wicked low cross from Malouda but appeared to damage his knee in the challenge with Andre Souza and was carried off just before the hour.
Franco di Santo was sent on in place of Malouda with 20 minutes remaining and almost headed Chelsea ahead with his first touch of the ball after stealing in unnoticed at the near post. Lampard headed the ball through for Anelka, who had just strayed offside but was then booked for high feet on the Cluj goalkeeper Eduard Stancioiu.
Cluj grew in confidence in the closing stages - and when Alex missed a long clearance, once again Chelsea were thankful Cech was alert to race off his line and beat Kone to the ball.
Trica cleverly worked himself some room on the edge of the Chelsea area and ignored Culio unmarked to the left and attempted to curl an effort into the top corner - which flew inches wide. After Juliano Belletti flashed a shot wide, Pereira launched another run from deep, linked with Kone and forced Cech to tip his shot around the post.
The Ivory Coast striker was carried off on a stretcher with an apparent knee injury early in the second half.
Despite Frank Lampard's best efforts, Chelsea could not break down the resilient CFR Cluj rearguard - and the battling Romanian double winners were good value for their draw.
Cluj are enjoying a dream debut season in the Champions League, having opened their campaign with a 2-1 win over Roma a fortnight ago, and they now sit level with Chelsea on top of Group A.
The stands shook as the Transylvanian locals greeted the teams by stamping their feet and unfurling a giant image of striker Juan Culio, who scored both goals in Rome, dressed as Dracula and tying a Cluj scarf around Big Ben.
Goalkeeper Petr Cech was called into action in the opening minute to beat Cluj midfielder Sebastian Dubarbier to a dangerous through ball.
Salomon Kalou scuffed Chelsea's first shot on goal, but it came from a promising build-up as Lampard linked neatly with Drogba on the edge of the Cluj box.
John Terry and Mikel John Obi made a hash of clearing a long punt forward but were let off the hook when Yssof Kone tried to lob Cech from 30 yards and floated his effort harmlessly over the bar.
It was a sign of things to come in the first half as Mikel struggled to dominate a limited Cluj central midfield, and Chelsea carelessly conceded possession.
When Florent Malouda did just that, Cluj raced forward - and Chelsea appeared vulnerable only for Culio to pick out Dubarbier in an off-side position.
Lampard was trying to conjure something up for Chelsea. Jose Bosingwa was a regular target down the right flank, but Cluj covered him well.
The Romanians then stepped up the intensity, forcing Chelsea on to the back foot as Alvaro Pereira repeatedly surged forward from left-back.
Periera slipped a pass to Kone, who lofted his cross over Terry's head and towards Eugen Trica. The midfielder attempted a spectacular volley but managed little more than an air shot.
Pereira then launched another incisive Cluj attack, halted only by Bosingwa's vital last-ditch tackle on the Uruguayan inside the Chelsea box.
Pereira charged forward again to meet Trica's lay-off, but his low drive flashed across Cech's goal and just wide.
Nicolas Anelka was sent on in place of Kalou at half-time as Chelsea switched to two up front and immediately looked more dangerous.
Bosingwa almost picked out Drogba, and Anelka then clipped a short ball towards Lampard at the near post - which the England midfielder could not quite squeeze home.
But Chelsea's change in formation did not last long. Drogba threw himself at a wicked low cross from Malouda but appeared to damage his knee in the challenge with Andre Souza and was carried off just before the hour.
Franco di Santo was sent on in place of Malouda with 20 minutes remaining and almost headed Chelsea ahead with his first touch of the ball after stealing in unnoticed at the near post. Lampard headed the ball through for Anelka, who had just strayed offside but was then booked for high feet on the Cluj goalkeeper Eduard Stancioiu.
Cluj grew in confidence in the closing stages - and when Alex missed a long clearance, once again Chelsea were thankful Cech was alert to race off his line and beat Kone to the ball.
Trica cleverly worked himself some room on the edge of the Chelsea area and ignored Culio unmarked to the left and attempted to curl an effort into the top corner - which flew inches wide. After Juliano Belletti flashed a shot wide, Pereira launched another run from deep, linked with Kone and forced Cech to tip his shot around the post.