Match Summary
Chelsea's hopes of qualifying automatically for the European Cup knockouts were suffered a setback as their Italian opponents fought back to win in their home stadium.
Both sides went into this fixture with the same records in the league phase of this year's competition, having secured three victories, drawn, and lost to have accrued 10 points.
For large parts there was very little to separate them in this contest too, even though Chelsea got their noses in front in the first half when the Brazilian converted the captain's cross.
But Atalanta always looked a threat going forwards, with former Premier League attacker causing issues for the defence.
James shot wide in the after the break but Atalanta raised the intensity and rightfully drew level when former West Ham United striker headed in a cross.
The winger hammered a powerful shot straight at the keeper but Atalanta secured the winning goal in the closing stages when the Blues defenders retreated from Charles de Ketelaere, who seized the opportunity with a driven finish.
Chelsea tried to rescue a point in stoppage time but a excellent stop by the Atalanta goalkeeper kept out Joao Pedro.
The final score means Chelsea slip out of the automatic qualification places—the spots that progress automatically for the knockouts—to 11th with two league phase fixtures remaining.
The Bergamo club, meanwhile, leap up to third place, three points clear of the Blues.
This was a hugely disappointing result for Chelsea as even a point was keeping them well placed to secure the top-eight finish they require to bypass the uncertainty of the play-offs.
But they lost focus in defence with seven minutes remaining and Atalanta took full advantage.
The Italian side are in rich vein of form at the moment so this was always going to be a challenging test for the visitors, but they will be annoyed to be leaving with nothing after taking the lead.
But the broader context is that this continues Chelsea's worrying run of results in all tournaments.
Since beating Barcelona 3-0 at the close of November they are now winless in their last four outings.
Manager Enzo Enzo Maresca enacted five rotations for this match as he continued his strategy of rotating players in and out of the first team.
The rotations here followed after he implemented the same number for the loss to Leeds United and six for the draw with Bournemouth prior to the trip to Atalanta.
Maresca will see rotation as essential as he tries to manage players' fitness and compete both at domestically and in Europe, but he insisted the central contingent of players remains the unchanged for crucial games.
"I believe tonight [in] the starting lineup we had eight or nine players who played against Tottenham Hotspur, Barcelona, and the Gunners," he commented.
"If you see the five alterations that we did relative to the previous game it is different but it involves the eight or nine players playing in that match.
"The ones who took to the field tonight are the ones who feature in almost all the matches."
Chelsea's next Champions League game sees them welcome Pafos on the coming Wednesday (20:00 GMT).
The Italian team, on the other hand, are at home to Athletic Club at the identical kick-off time.