It was Zlatan Ibrahimovic's fancy footwork the drew a stunning save from Thibaut Courtois and the subsequent block by Cesar Azpilicueta from Ezequiel Lavezzi's fierce low shot that finally made them believe. It took just under an hour, but the crowd at the Parc des Prince were up on their feet and making themselves heard.
Before then, there was a sense that Chelsea were doing the kind of professional job one has come to expect from a Jose Mourinho team playing away in the Champions League. But the Special One's mark isn't all over this team like it was in his first spell, not by a long way - something the PSG were able to exploit once they started to believe.
The warning signs that this Chelsea may just be a little soft at its core were there just before Edinson Cavani's equaliser after Branislav Ivanovic had nudged home his 30th goal in a blue shirt. John Terry mopped up at the back as Cavani threatened to dart in, only to skew his clearance for the Uruguayan to collect the ball and start again.
Azpilicueta, usually a model of consistency looked vulnerable, and the much-maligned Gary Cahill followed suit. His frustration - all fist-clenching fury and screams - after Cavani's goal said it all.
Before then PSG had threatened to counter quickly. Chelsea looked so calm in possession but were panicked as the home side stepped on the gas. Two times in the first 45 minutes PSG cut straight through Chelsea, upping the tempo and causing problems only to misplace the final pass. Still, the baby-faced Marco Verratti prowled and probed and would come to the fore as the game's most prominent player in the second half.
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That forced Chelsea to retreat deeper into their own half, which made it all the more surprising when Ivanovic turned home Cahill's flick from Terry's cross - not exactly the most likely attacking combination. That was after 36 minutes, and it was the first shot on target for either team all night.
The second half belonged to PSG and after that galvanising moment 60 minutes in Chelsea looked like a wobbled boxer, groping around for relief and longing for the bell. Edinson Cavani danced through the Chelsea backline again and should have scored with 15 minutes to go. David Luiz, who relished taking centre-stage, threatened from close range and the Parc des Prince responded.
Laurent Blanc clasped his head in anguish as Zlatan Ibrahimovic's close range header was clawed away by Thibaut Coirtois seconds before the final whistle too. Salvatore Sirigu was untroubled at the other end from the moment he picked the ball out of the net in the first half.
PSG haven't lost in Europe at home since 2004 and in any competition in nine months. They looked strong this evening, nothing like the band of mercenaries longing for the beaches of summer that Chelsea had been promised. Thiago Silva had a rusty Diego Costa in his pocket, dealing with long ball after long ball with ease. Eden Hazard flitted and threatened, Cesc Fabregas and Ramires offered little in the fight for midfield.
Verratti was his side's conductor with the ball and the hound when Chelsea were in possession. Even Luiz, arguably at fault for the Chelsea goal, grew into the things and was enjoying himself in midfield by the end.
Indeed the game had a similar feel to the meeting between the pair last season that ended in a 3-1 victory for the Ligue 1 champions. The only difference this time was Courtois. He was worth more than two goals, pulling off a strong save from Ibrahimovic and Matuidi in the first half before his heroics in the second.
Given the chance at the start of the night, Mourinho would have happily taken a draw with an away goal tucked in his top pocket for the second round at Stamford Bridge at the start of next month. Mourinho complained afterwards that he had five players who couldn't train in the lead up to the game which makes the result seem all the better.
But despite that, tonight's game offered further evidence that all is not exactly as it should be with Chelsea. The result makes it just six wins from their last 12 games. If there's been one criticism of Chelsea - and that's all there really should be for a team seven points clear at the top of the Premier League - is that they've not yet hardened into the serial, relentless winners Mourinho wants them to be.
The Chelsea boss says that game is now a 'one leg game', or a showdown. Three weeks from now that theory will be put to the ultimate test.