An Emirates FA Cup Fourth Round replay is all that separates Millwall from another potential matchup with Premier League heavyweights Spurs.
Ben Thompson rescued The Lions with a late equaliser against League One Dale at The Den last week, meaning it will be all to play for at Crown Oil Arena in the replay on Tuesday night.
The winner of the tie will host either Newport County or Tottenham, the club that ended Millwall's Cup run in the Quarter Final last year.
"Rochdale is an important game for us," Harris told millwallfc.co.uk.
"I was disappointed with our performance in the first game against them, I have to be honest.
"We were poor mentally in the first hour and then completely dominated in the last half hour and should have won the game. I want to get through that tie and there is a carrot at the end of it - for both teams.
"The winner will host Spurs or Newport and I want my players to experience Tottenham at home at The Den, but we have to get through this tricky one first.
"Conditions won't be good so I will have to pick a team accordingly to win the game. Then we have a massive game against Cardiff in the League on Friday night under lights.
"We are preparing for those two sides and our squad will be really important."