Key Moments
Chelsea's chances of qualifying automatically for the European Cup knockout stages were suffered a setback as their Italian opponents fought back to triumph in Bergamo.
The two teams entered this game with identical points tallies in the league phase of this season's tournament, having secured three victories, tied one, and suffered one defeat to have accrued 10 points.
For large parts there was little to distinguish them in this contest too, although Chelsea took the lead in the opening 45 minutes when the Brazilian converted the captain's delivery.
But The Serie A side consistently appeared a danger going forward, with former Charlton and Everton attacker creating problems for the backline.
James fired wide in the second half but Atalanta upped the intensity and justly drew level when former West Ham United striker Gianluca Scamacca a cross.
The winger hammered a strong effort straight at the goalkeeper but Atalanta got the winner in the closing stages when the Chelsea defenders retreated from Charles de Ketelaere, who seized the opportunity with a low strike.
The visitors tried to rescue a point in stoppage time but a brilliant stop by Marco Carnesecchi denied Pedro.
The outcome means Chelsea drop out of the automatic qualification places—the positions that qualify automatically for the next round—to 11th with two group stage matches left to play.
The Bergamo club, in contrast, jump up to third, three points ahead of the Blues.
This was a hugely disappointing outcome for Chelsea as even a draw was leaving them well placed to achieve the top eight position they need to avoid the uncertainty of the play-offs.
But they lost focus in their defensive duties with seven minutes remaining and their opponents took full advantage.
The Italians are in rich vein of form at the moment so this was always going to be a difficult test for the Blues, but they will be annoyed to be departing with no points after securing the early advantage.
But the bigger picture is that this extends Chelsea's troubling sequence of results in all competitions.
Since defeating the Spanish giants 3-0 at the close of November they are now winless in their last four games.
Manager Enzo Enzo Maresca enacted five changes for this game as he persisted with his policy of moving players in and out of the first team.
The rotations here followed after he made the same number for the defeat to Leeds and six for the tie with Bournemouth prior to the trip to Bergamo.
The coach will see squad rotation as necessary as he tries to manage players' workloads and challenge both at home and in Europe, but he maintained the core group of players remains the same for key games.
"I think tonight [in] the starting lineup we had eight or nine players who played against Tottenham, Barcelona, and the Gunners," he commented.
"If you look at the five changes that we made relative to Bournemouth it is a change but it involves the eight or nine players who played Barcelona.
"The ones who took to the field this evening are the individuals who feature in almost all the games."
The Blues' next Champions League game sees them welcome Pafos on Wednesday, 21 January (8pm GMT).
The Italian team, on the other hand, host Athletic Club at the same time.
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