Hull manager Steve Bruce admitted his side were taught a valuable lesson by Beligan outfit Lokeren after goalkeeper Allan McGregor's blunder saw them fall to a 1-0 defeat in the first leg of their Europa League qualifying play-off tie on Thursday night.
Hans Vanaken was the lucky recipient of McGregor's blunder as he was in the right place at the right time as the former Rangers stopper passed the ball straight to him, allowing the 32-year-old to round him and roll the ball into the net.
Defender James Chester came agonisingly close to making it 1-1 in the 89th minute but he missed the target with a free header from Sone Aluko's cross meaning the Belgian side will take the advantage into the return leg at the KC Stadium.
"We have learned the first lesson of what we are playing in Europe and that is concentration," Bruce said.
"We made a mistake which cost us the game. Our 'keeper saved a penalty last Saturday against QPR but today he made a mistake and it's an awful way to lose the match.
"We were very comfortable in the game. We had four good chances to score but we didn't and then he made a mistake in the second half then they got after us much quicker than in the first half."
Bruce knows overhauling the one-goal deficit could prove to be tricky even though the second leg is on Humberside, and he again reiterated that Lokeren are not a team to be taken lightly.
"It's going to be difficult in the return leg," the Hull boss said.
"I have never said that Lokeren was going to be a breeze because no game in Europe is. Lokeren were fifth in the league, they won the cup and they have good players.
"Now we have to try and win the game at home but the difficulty is that we don't have an away goal. I know it will be a full house so we have to win it before our crowd and we have to qualify."
Hull striker Sone Aluko was also left to rue the costly mistake by McGregor.
"We had a very good game today but it is a pity that we lost," Aluko said.
"We had some good chances but we still conceded a goal through a mistake. I think Lokeren have a good team. T hey are very well organised and they played a good game.
"We tried to come back but we didn't get the goal so we are disappointed tonight to lose here."