The Blues host Manchester United on Saturday and then visit the Seagulls on Tuesday.
They are currently only two points ahead of Albion and are sixth in the table as they chase a Champions League spot.
Head coach Rosenior, the former Albion full-back, said: “As the season goes on, the less games you have left, the more important the games become.
“We have to take advantage of this moment. We’re running out of time.
“We need to show that initiative on Saturday and play on the front foot and make up those points, which is still definitely possible.
“If I look at each game, I think it’s just come down to loss of concentration of focus in a moment that then has snowballed into the rest of the performances.
“What we have to do is manage the margins of the game a little bit better.”
A fans’ protest is planned ahead of the United game
Rosenior said: “Every supporter has their viewpoint.
“Every supporter wants their club to do well and to win games. Our job, my job, is to produce those results in the long term.”
Former Albion loanee Levi Colwill set to take part in an under-21 game on Friday as he continues his recovery from an anterior cruciate ligament injury, with a hope that he could make his first-team comeback before the end of the campaign.
Rosenior said: “Levi is an outstanding player and a leader in the dressing room.”