Albion's manager was left to rue some costly errors.
Brighton & Hove Albion boss Chris Hughton said mad moments cost his side as they crashed out of the FA Cup at Lincoln City
Albion led at the break thanks to Richie Towell's well-taken goal, but Lincoln hit back after the interval for a shock win.
Hughton told seagulls.co.uk, "It's a result I couldn’t see coming, especially at half time. They are a big, strong side full of energy and are very direct.
"These are things that you have to cope with, but I thought in that first-half period we coped with it and we had our moments. What we spoke about at half time was not giving them lift of enthusiasm that they needed.
"We felt at half time they had a bit of a tailwind going in their favour, but I still felt on the balance of play we would cope with them very well, and we did, but we had some mad moments.
"We did have those mad moments and it gave them the lift they needed, certainly the penalty got the crowd going and they were three very poor goals we conceded.
"It was a team good enough to win the game. The mistakes could've been made by any one of the players that played in the last league game. These are elementary mistakes and we have to learn from it.
"We're incredibly disappointed and irrespective of whether it's against a National League side, this is a very difficult place to come.
"We wanted to stay in the cup. Credit to them I hope they get a good draw, but it's an incredibly disappointing day."
Hughton feels debutant Fikayo Tomori, who put through his own goal shortly after Lincoln had levelled from the penalty spot via Alan Power, will learn from the experience.
"It has been a tough day for us and these are the ones you have to be able to take on the chin. You want to be better for it in the next games, and it doesn't matter who the opposition are, if you don't play well enough and make mistakes you will lose the game."
Meanwhile Hughton will be hopeful Niki Maenpaa's injury isn't as bad as he first feared.
"It was certainly bad enough for him to come off. At the time we thought it might be dislocated, but now I don’t think it is. The extent of it, we'll find out, but I don't think it's dislocated."