There will be questions about whether Rosenior got his starting XI wrong, having made wholesale changes from the 3-2 win at Napoli.
Chelsea‘s entire left side – Alejandro Garnacho, Jorrel Hato and Benoit Badiashile – could arguably be blamed for Jarrod Bowen’s opening goal and Crysencio Summerville’s second for West Ham.
All three were taken off at half-time, despite an enforced earlier change when Jamie Gittens was replaced by Pedro Neto midway through the first half.
Rosenior said: “The individuals came off and then people will look at them. That wasn’t on them. There was a collective poor performance in the first half.
“Those players know with me, I make early changes. It doesn’t mean that all of a sudden they’re out of my thoughts at all.”
Early changes have become one of the defining characteristics of Rosenior’s management at Chelsea, as was also the case at sister club Strasbourg, which is likewise owned by Todd Boehly and Clearlake Capital.
Against Brentford, early substitutions helped Chelsea protect a narrow lead before a late goal secured a 2-0 victory in his first league match.
Despite a poor performance on Saturday, Garnacho has credit in the bank after scoring two goals from the bench against Arsenal in the first leg of their Carabao Cup semi-final, while Cole Palmer set up Joao Pedro twice as a substitute in Naples.
Joao Pedro highlighted in his Sky Sports interview that Chelsea have a “strong squad”, while ex-Liverpool midfielder Jamie Redknapp added after Saturday’s win: “If you ask every single Chelsea fan, it was the easiest set of substitutions you’ll ever have to make.”
There is depth in terms of numbers, but changes such as Cucurella, Joao Pedro, Wesley Fofana, Neto and eventually Reece James – all among Chelsea‘s strongest performers – were always likely to influence the match when introduced from the bench.
However, it has proven challenging to keep Chelsea competitive when resting players.
It was a criticism Maresca made of the squad after a 3-1 defeat by Leeds when, like Rosenior against West Ham, he rotated heavily. He said that players such as Andrey Santos and Tosin Adarabioyo were not at the “level” of his first-choice starters.
Former Chelsea goalkeeper Rob Green echoed that view on BBC Radio 5 Live, saying: “Rosenior righted the wrongs in the second half, but he’s got the same problems now as Enzo Maresca.
“The players who are not in the starting XI are so far off the starting XI. So he’ll be delighted, but also at the back of his mind, he’s got a problem.”
Rosenior is just the fourth English manager to win his first three Premier League games.
He has won six of his first seven matches in all competitions and has overseen Chelsea‘s first comeback from two goals down to win a Premier League match.
Those results have propelled the Blues to fourth place while competing on four fronts domestically and in Europe.
They will need another comeback win at Arsenal on Tuesday in the second leg of their League Cup semi‑final (20:00 GMT), having lost the first leg 3-2 at Stamford Bridge.