Michael Jolley felt his Grimsby side were prevented from getting into their rhythm by Chesterfield at the Proact today.
Jolley was over the moon to book a place in the third round, with its potential glamour ties, but admitted his side can and have played better than they did today.
"We're really happy, because it's not a frequent thing for Grimsby to be in round three.
"I think over the piece we deserve to be, but we're conscious we can play better than that.
"Certainly from the levels we've set recently, we didn't play well enough with the ball.
"It was a professional job, we scored two goals and kept a clean sheet, so we'll take it."
Jolley said Chesterfield's style of play caused Grimsby problems, the Spireites dominating parts of the game territoriality and enjoying the lion's share of possession.
"It was a tight game, they play a certain style of play which is difficult to deal with, difficult to play against," said Jolley.
"It prevented us from getting any flow or rhythm to our game.
"We weren't happy at half-time, we didn't think we played very well in the first half.
"We spoke about that with the players and they understood how we felt, they felt similarly.
"Even in the second half we didn't really get to the level we can get to.
"But we've got to give Chesterfield some credit, they're fighting to get through like we are and they made it a certain kind of game.
"That prevented us from getting going 100 per cent, but I think we saw it out relatively well and got stronger as it went on."