John Gregory admitted Crawley learned a harsh lesson as they went down 2-0 to Sheffield United at the Checkatrade.com Stadium.
Reds enjoyed the majority of the possession and created more chances but ended up empty handed thanks to goals from Conor Coady in each half.
Coady pounced on a mistake by Kyle McFadzean to give the Blades the lead against the run of play in the 18th minute.
The midfielder then volleyed home a cross by Jamie Murphy early in the second half after Dannie Bulman had given away possession.
Gregory said: "It was two mistakes to nil wasn't it. They had five attempts on goal and scored two of them and we must have had about 17 and didn't score.
"We even had to warm (goalkeeper) Paul Jones up at half-time because he was so cold through inactivity. He was even less active in the second half but still ended up picking the ball out of his own net twice.
"I was a bit disappointed with us in the last third of the pitch. Up until the final third we were excellent but we lacked that spark where it matters.
"There were lots of positive to take from the game though but we need to improve in the key areas."