At a Glance
The London club's hopes of securing a place automatically for the Champions League knockouts were hit hard as their Italian opponents came from behind to triumph in Bergamo.
The two teams went into this match with matching records in the initial stage of this year's tournament, having secured three victories, tied one, and suffered one defeat to be on ten points.
For extended periods there was very little to distinguish them in this contest too, although Chelsea took the lead in the first half when the Brazilian finished the captain's delivery.
But Atalanta consistently appeared a threat going forwards, with ex- Charlton and Everton attacker Ademola Lookman issues for the defence.
Reece James fired wide in the second half but Atalanta raised the pressure and deservedly drew level when former West Ham United striker headed in a centering pass.
Alejandro Garnacho hammered a powerful shot straight at the keeper but Atalanta got the winner in the closing stages when the Blues defence retreated from the midfielder, who made no mistake with a low shot.
Chelsea attempted to rescue a point late on but a excellent save by the Atalanta goalkeeper kept out Pedro.
The outcome means Chelsea slip out of the top eight—the positions that progress automatically for the knockouts—to eleventh with two group stage fixtures remaining.
Atalanta, meanwhile, climb up to third, three points ahead of the Blues.
This was a hugely frustrating result for Chelsea as even a draw was leaving them well placed to achieve the top-eight position they need to avoid the lottery of the play-offs.
But they lacked concentration in their defensive duties with seven minutes left on the clock and Atalanta seized the moment.
The Italian side are in rich vein of form at the moment so this was always going to be a tough examination for the visitors, but they will be frustrated to be departing with nothing after taking the early advantage.
But the wider issue is that this extends Chelsea's troubling streak of form in all competitions.
Since beating the Spanish giants 3-0 at the close of November they are now without a win in their last four matches.
Manager Enzo Maresca made five alterations for this match as he persisted with his policy of rotating players in and out of the starting lineup.
The changes here came after he implemented the same number for the defeat to Leeds United and six for the tie with AFC Bournemouth prior to the journey to Atalanta.
Maresca will see rotation as essential as he tries to manage players' workloads and challenge both at home and abroad, but he stated the key nucleus of players remains the unchanged for important games.
"I think in this match [in] the starting lineup we had eight or nine players who played against Tottenham, FC Barcelona, and Arsenal," he stated.
"If you see the five changes that we did relative to the previous game it may be different but it is the same eight or nine players playing in that match.
"The ones who played tonight are the individuals who feature in almost all the matches."
Chelsea's next Champions League fixture sees them host the Cypriot side on Wednesday, 21 January (20:00 GMT).
Atalanta, meanwhile, host Athletic Club at the identical kick-off time.
Elara is a seasoned betting analyst with over a decade of experience in sports gambling and data-driven strategy development.
Joyce Gomez
Joyce Gomez
Joyce Gomez