Under-21s coach Calum McFarlane oversaw a draw to Manchester City and a loss to Fulham after the sacking of Enzo Maresca and will now step aside for Rosenior, who takes the reins.
What is Rosenior's biggest challenge?
Rosenior will hope to start life in West London with a bang as he first opened up on the biggest challenge he faces as Chelsea boss.
"I think the biggest challenge in any club in any team is to create the right culture, the right spirit and the right values.
"The talent levels I have seen over the last few days - the ability levels are world-class.
"The previous coach Enzo (Maresca) has done a good job tactically and it is my job to take it to the next level and me and my staff are going to work very hard to do that."
"I think the turnover of managers now is huge. The pressure is there from day one and if I wasn't willing to take on that pressure and privilege I wouldnt' be here."
People want to feel apart of something
Rosenior left Chelsea’s sister club Strasbourg with a 49.2% win record from 63 games, and was next asked about the differences between French and English football as a manager who has coached in both countries.
"Not much. The language and culture - France is a beautiful country and it is a fantastic league. PSG won the Champions League last season and I won many games there.
"When you connect with people, they all have the same needs, everyone wants to feel they are part of something and that's what I want to create here."
Focus on winning the next game
Chelsea are aiming to lift the FA Cup for the ninth time in their history and for the first time since 2018 and history is on their side as the Blues have advanced from 61 of their last 63 FA Cup ties against lower-league opposition, including their last 22 in a row. Rosenior opened up on the clash and their harsh fixture list that lays ahead.
"I've said to the players, focus on winning the next game. That's how we go on a run. The talent we have, the engagement to something new, there's really positive signs. The potential for this club is limitless, and I won't limit limitlessness.
"It's a tough run, it's a tough league. We aren't the only club that'll go through difficult periods, every club does. Sometimes a different voice helps, but we aren't far way and that's really important for the players to know."
"I'm so fortunate to work with some outstanding players. I'm paid well. Pressure is a privilege. There are loads of people who would want to be in my shoes, and I try remember that every day."
Lastly, Rosenior suggested that he wants to prove many of the media wrong much like he did in France: "When I went in at Strasbourg I was a joke in the media and they said that my team would finish last. I was a nobody from England and we finished three points off the Champions League places. The noise is just noise.
"I am not promising it, but I am working towards it and I believe strongly we can be very successful here."