The Republic of Ireland midfielder made no bones about his side's fatal errors on Sunday, while team-mate Simon Cox was similarly gutted by their deficiencies against the Croats
Mario Mandzukic was left unmarked to open the scoring with a looping header inside just three minutes, before a sliced Stephen Ward clearance gifted another and the Wolfsburg attacker scored his second via another cross.
"We lost goals at wrong time and that hurt us, we made mistakes at the schoolboy level and shot ourselves in the foot," admitted Andrews.
"Croatia are a decent side, we were under no illusions, it was not the case of our confidence and even you could see how we responded on the pitch.
"We wanted to do it for the fans, they were unbelievable throughout the day, at the hotel and here, being so loud in the rain for 90 minutes.
"The boys feel a bit flat at the moment but will be back up tomorrow, and this is football , when there is a chance you have to take it, there will be lot of effort from us.
"We will look at this game, see what we made wrong, where we can improve and how to do it on Tuesday in the training.
"I think we have enough time to prepare well, despite that Croatia showed us how to play well.
Andrews then reflected on the build-up to the Jelavic's second goal for Croatia, where various Ireland players felt the referee should have flagged offside. However, he insists his protest was for a foul on Stephen Ward.
"I wasn't appealing for an offside at the second goal, I was appealing for a foul on Stephen Ward, I didn't have an angle to see it, though few people told me it might have been one.
"But I felt it was a foul, he didn't clear the ball because he was tripped. We had our chances in the second half, we thought we should have a penalty and myself I couldn't direct the header into the net.
Meanwhile, his West Brom team-mate Simon Cox was similarly downbeat about Ireland's performance, claiming an early "sucker punch" put their eventual efforts in the contest in vain.
"It took them only three minutes to score and that was always something we said ourselves to look out for and we have always said to ourselves to be hard to beat.
"Into the first game and we fell to a sucker punch. I've played for most of the season at West Brom on the left side, it wasn't new to me.
"One of the biggest atmosphere for me, even in the end they were cheering up. We still created in the last ten minutes, being more direct and at the end we pushed them back
"The main task was to attack more, try to get to the end, cross and after all enjoy myself.
"Whether we will train tomorrow is up to the boss, maybe we will have a cool down and then we will look at Spain, the best in the world and that game now means as much to us.
"At the end of the day, you don't go to such tournaments thinking you will have easy games, do you? If you're going to progress you have to be a good side and that is exactly how we have to present ourselves."