Midda struck again from the spot before captain Gidi Amar headed Leeds into the last-eight.
Kristall said: "Considering we were playing a good side without some of our key players, this win was the best team display we have put in this season.
"We carried our momentum on from the league programme to this cup game. Confidence is important.
"We looked like a side who have been winning games while they have been struggling in their league."
Leeds need just a point at Heaton Park Rovers to be crowned champions on Sunday.
They will also be boosted with Richard Black and Rob Selwyn set to return after missing the cup clash in the capital.
Kristall said: "We know what we have to do. It’s a case of us concentrating on what we have done all season."
