"We can't have any negative thoughts at all," he said. "We've got to approach it very positively.
"There shouldn't be any need for me to be motivating people. The motivation is there with the prize of a game at one of the best stadiums in the world. There's plenty to play for.
"It's a tough ask and it's going to be nail-biting, but we go away from home, the shackles come off and the pressure is put on Carlisle. And we can absolutely get better.
"There's going to be a presence of Leeds United fans and they'll be giving it their best, but it'll be predominantly Carlisle fans so the onus is on the home side. We've got to take advantage of that if that affects Carlisle."
The injury-time goal produced by Dougie Freedman has altered the balance of a tie which Carlisle were looking in complete control of.
"Psychologically for our players it was important," McAllister added. "I don't know how it's affected Carlisle, but for us it was a boost.
"I felt that my players gave their all and the effort was there. It was just a bit misdirected and the quality I know they've got didn't come to the fore.
"But I think it'll be different tonight and I'm looking forward to seeing five or six of my players performing better. This is it."