Match Summary
Chelsea's ambitions of securing a place automatically for the European Cup knockouts were suffered a setback as their Italian opponents fought back to triumph in Bergamo.
Both sides went into this fixture with matching points tallies in the initial stage of this year's competition, having won, drawn, and lost to sit on 10 points.
For large parts there was not much to choose between them in this encounter too, even though Chelsea got their noses in front in the first half when the Brazilian turned in Reece James' delivery.
But The Serie A side consistently appeared a threat going on the attack, with former Charlton and Everton attacker Ademola Lookman issues for the backline.
Reece James fired wide in the second half but Atalanta raised the pressure and rightfully drew level when ex-West Ham striker nodded home a centering pass.
Alejandro Garnacho hammered a strong effort straight at the keeper but they got the winner in the closing stages when the Chelsea defence backed off Charles de Ketelaere, who made no mistake with a powerful finish.
The visitors tried to rescue a draw in stoppage time but a brilliant stop by Marco Carnesecchi kept out Joao Pedro.
The outcome means Chelsea drop out of the automatic qualification places—the positions that qualify automatically for the knockouts—to 11th with two group stage games left to play.
The Bergamo club, in contrast, leap up to third place, three points ahead of the Londoners.
This was a extremely frustrating result for Chelsea as even a point was leaving them in a strong position to achieve the top-eight finish they require to bypass the lottery of the play-offs.
But they lacked concentration in defence with seven minutes remaining and Atalanta seized the moment.
The Italian side are in good form at the moment so this was always going to be a tough examination for the Blues, but they will be disappointed to be departing with no points after taking the lead.
But the broader context is that this continues Chelsea's worrying streak of results in all tournaments.
Since beating the Spanish giants 3-0 at the close of November they are now winless in their last four outings.
Manager Enzo Enzo Maresca made five changes for this game as he continued his strategy of rotating players in and out of the starting lineup.
The rotations here followed after he made the identical amount for the defeat to Leeds and six for the tie with Bournemouth prior to the journey to Atalanta.
The coach will see squad rotation as essential as he attempts to handle players' fitness and challenge both at home and abroad, but he insisted the key nucleus of players stays the unchanged for key games.
"I believe tonight [in] the first XI we had eight or nine players who featured against Tottenham, FC Barcelona, and the Gunners," he commented.
"If you see the five alterations that we did compared to Bournemouth it may be different but it involves the eight or nine players who played in that match.
"The players who played tonight are the ones who feature in almost all the games."
The Blues' next Champions League fixture sees them welcome Pafos on Wednesday, 21 January (8pm GMT).
The Italian team, on the other hand, host Athletic Bilbao at the identical kick-off time.
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