A Berlin-based political analyst with a decade of experience covering European affairs and a passion for investigative journalism.
Key Moments
The London club's hopes of securing a place automatically for the Champions League knockouts were dealt a blow as their Italian opponents came from behind to claim victory in their home stadium.
Both sides went into this match with matching records in the league phase of this year's tournament, having secured three victories, drawn, and suffered one defeat to have accrued 10 points.
For extended periods there was not much to choose between them in this encounter too, even though Chelsea took the lead in the first half when Joao Pedro turned in the captain's cross.
But Atalanta remained a threat going forward, with former Charlton and Everton attacker causing problems for the backline.
Reece James shot wide in the second half but the home team increased the pressure and justly levelled when ex-West Ham striker headed in a centering pass.
Alejandro Garnacho drove a powerful shot straight at the goalkeeper but they secured the decisive strike late on when the Chelsea defenders retreated from the midfielder, who seized the opportunity with a powerful finish.
Chelsea tried to salvage a point late on but a brilliant save by the Atalanta goalkeeper kept out Pedro.
The outcome means Chelsea slip out of the top eight—the spots that qualify automatically for the next round—to 11th with two group stage fixtures left to play.
Atalanta, meanwhile, jump up to third place, three points ahead of the Blues.
This was a hugely frustrating result for Chelsea as even a point was keeping them well placed to secure the top-eight position they need to avoid the uncertainty of the play-offs.
But they lost focus in defence with seven minutes left on the clock and Atalanta capitalised completely.
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 leaving with nothing after taking the early advantage.
But the wider issue is that this extends Chelsea's worrying streak of form in all competitions.
Since defeating Barcelona 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 continued his strategy of rotating players in and out of the starting 11.
The changes here followed after he made the identical amount for the loss to Leeds United and six for the draw with AFC Bournemouth prior to the journey to Atalanta.
Maresca will view squad rotation as vital as he attempts to manage players' workloads and challenge both at domestically and in Europe, but he insisted the key nucleus of players stays the same for crucial fixtures.
"I believe tonight [in] the starting lineup we had eight or nine players who played against Tottenham Hotspur, FC Barcelona, and Arsenal," he said.
"If you see the five changes that we made relative to Bournemouth it may be different but it is the eight or nine players who played Barcelona.
"The players who took to the field this evening are the ones who feature in almost all the games."
The Blues' next Champions League game sees them welcome the Cypriot side on Wednesday, 21 January (20:00 GMT).
The Italian team, on the other hand, host Athletic Club at the same time.
A Berlin-based political analyst with a decade of experience covering European affairs and a passion for investigative journalism.