"We haven't had a run for a long time, two or three years, as we had some bad draws of course. We're at home and we have got to take advantage of that. If we get through, we have got another home tie [against Blackpool or Fulham] so there's a big incentive for the club to make sure we get through."
The replay will come too soon for Jonny Evans, who missed the victory against Liverpool after feeling his hamstring in training over the weekend.
"I could risk Jonny," admitted Sir Alex. "But I'm looking at Sunday's game [at Tottenham] for him."
The full exclusive interview with Sir Alex will appear in MUTV's Matchday Live, this Wednesday at 16:00 and 19:00. To subscribe, visit manutd.com/joinmutv.