Match Summary
Chelsea's chances of securing a place automatically for the European Cup knockouts were suffered a setback as their Italian opponents came from behind to claim victory in their home stadium.
The two teams went into this match with the same records in the league phase of this season's tournament, having won, drawn, and lost to be on 10 points.
For much of the game there was very little to distinguish them in this contest too, even though Chelsea got their noses in front in the first half when the Brazilian finished the captain's cross.
But The Serie A side consistently appeared a threat going forward, with former Charlton and Everton attacker causing issues for the defence.
James shot wide in the after the break but the home team raised the intensity and rightfully levelled when ex-West Ham striker headed in a centering pass.
Alejandro Garnacho hammered a strong effort straight at the keeper but Atalanta scored the winner in the closing stages when the Chelsea defence retreated from the midfielder, who seized the opportunity with a low shot.
The visitors tried to rescue a point late on but a brilliant save by Marco Carnesecchi kept out Joao Pedro.
The final score means Chelsea slip out of the automatic qualification places—the spots that qualify automatically for the next round—to eleventh with two league phase matches left to play.
Atalanta, in contrast, climb up to third place, three points ahead of the Blues.
This was a deeply frustrating result for Chelsea as even a point was leaving them in a strong position to achieve the top eight finish they require to avoid the uncertainty of the qualifying play-off round.
But they lost focus in defence with seven minutes remaining and Atalanta seized the moment.
The Italians are in good form at the moment so this was always going to be a difficult test for the Blues, but they will be disappointed to be departing with nothing after securing the lead.
But the wider issue is that this extends Chelsea's concerning run of results in all competitions.
Since defeating Barcelona 3-0 at the end of November they are now without a win in their last four matches.
Chelsea boss Maresca enacted five changes for this game as he continued his run of rotating 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 AFC Bournemouth prior to the journey to Atalanta.
The coach will view squad rotation as necessary as he attempts to manage players' fitness and challenge both at domestically and in Europe, but he insisted the core group of players remains the same for crucial games.
"I believe in this match [in] the first XI we had eight or nine players who featured against Tottenham Hotspur, Barcelona, and Arsenal," he stated.
"If you see the five changes that we made compared to the previous game it may be different but it involves the same eight or nine players playing in that match.
"The players who took to the field this evening are the individuals who feature in almost all the games."
Chelsea's next European 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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