Two goals from Scott Sinclair and one from sub Emil Riis saw the Lillywhites through, but they had to weather a good first half from the Stags before Sinclair netted a superb goal just before the break.
“Mansfield are a good team and the pitch is a bit tight so we knew we'd be in for a tough game,” he said.
“We had a great opportunity but the keeper made a good save and that was our only clear cut opportunity we'd created in the first half.
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“But we managed to get the break just before half-time with a great pass from Sean (Maguire) who sliced Scottie (Sinclair) through for a fantastic finish which gave us a wee bit of breathing space at half time.
“First half we needed to do better, but we were miles better in the second half.
“Second half we knew we needed that second goal as when you go to teams that are in lower divisions than yourself it is difficult. There are no easy games.”
He added: “Once we got the second goal we showed a bit of class. We managed to retain the ball, move it, probe and the third goal was the icing on the post.
“I am delighted all round and delighted for our supporters who turned up in numbers tonight.
“We were disappointing on Saturday so it was important to win tonight and get in the draw for the next round and we accomplished that.”