The Blues were second best throughout at Hill Dickinson Stadium, where two goals from Beto and a superb finish by Iliman Ndiaye sealed a comprehensive victory for the hosts. The result extended Chelsea's losing streak to four matches in all competitions and compounded the fallout from their heavy Champions League exit at the hands of Paris Saint-Germain.
Rosenior did not hide his frustration, describing the performance as unacceptable and far from what had been discussed internally.
"The most disappointing evening so far in terms of the things we've spoken about - not gifting goals away, making sure we're in the game, getting control of the game," he said. "It wasn't there and it turned into a really, really difficult evening where the result and performance was nowhere near what we expected or wanted."
Despite enjoying spells of possession and territory, Chelsea once again failed to convert promising moments, and defensive lapses proved decisive. Rosenior pointed to a recurring pattern that has hurt his side in recent weeks. "For me, we arrived into the final third a lot… we were arriving and creating moments which we don't take. We're not clinical enough. Then out of nowhere, it feels like out of nowhere, they score. It's not the first time that that's happened," said the Blues boss.
The defeat could have been even more costly in the race for Champions League qualification. With rivals dropping points elsewhere, Chelsea had an opportunity to strengthen their position but instead remain sixth, just outside the top four with the season entering its final stretch. Having won only one of their last six league matches and failed to score in three consecutive games, momentum has clearly slipped at a crucial time.
While criticism has intensified, Rosenior pushed back against suggestions that the team's struggles are rooted in tactical shortcomings. "It is not a tactical thing," he insisted. "I want to protect my players always… but that's what it is. That's happened too many times in my time recently for me not to tell the truth as it is." He also rejected the idea that effort is lacking within the squad, adding: "I don't think there's a lack of effort. I don't think there's a lack of belief or determination in the team."
Instead, he framed the issues as a combination of individual errors, confidence dips, and the psychological toll of a demanding schedule. "If you're a logical thinking person and you look at the workload and the amount of games that the players have played, I think it's a pretty simple conclusion to come to," he said, while stressing he did not want to make excuses.
The Chelsea boss also called for perspective amid growing external criticism. "I'm learning about this club. It's a massive club. There's been a lot of noise, a lot of negative noise, rightfully so," he admitted. "We've had 10 games in the league together as a group, we've got 17 points… so we have to forget the noise. We have to keep our confidence and our composure."