Moises Caicedo broke the deadlock on 78 minutes to earn the 1-0 win at Stamford Bridge.
Rosenior said afterwards: "Yeah, you have to keep banging on the door. Obviously, you want to get the breakthrough earlier to open up the game. That was a harsh decision on Enzo (Fernandez). Maybe puts his hands on him (for the disallowed goal). I think in the Premier League, it's probably a goal.
"But the players, sometimes you just have to keep going. You have to keep knocking on the door, but you also have to keep the back door shut. There were things I was pleased with. There were things that we need to improve on. But overall, the body language of the group, they kept going.
"They were making block after block and save after save. I was delighted for Moi (Caicedo) to get the goal and get the result we deserved."
Indeed, on Caicedo's goalscoring form, Rosenior continued: "Yeah, Moi is an outstanding player. A world-class midfield player. I don't know how many headers he's actually scored in his career, but we're always a threat on set plays. He's a top player.
"But no, when you play against a low block, your pivot players can be higher up the pitch. He's scored a couple from outside the box this season. And hopefully, he can keep chipping in with goals to help us win more games of football."
Rosenior also explained why he took off captain Reece James at halftime. The manager insisting it was all about managing the fullback's minutes and fitness.
"Yeah, minutes. And making sure that he's prepared for we're playing Wednesday, Saturday, Wednesday, Saturday. And I want to make sure Reece is available as much as possible because he's an outstanding player and he's a leader in our group."