Moors lost 2-0 at FC Halifax and blew the chance to return to the top of the National League table.
They stay second on the same number of points as leaders Leyton Orient but have now played two games more.
Flowers said his ten men needed to be more streetwise as they went down to defeat at the Shay.
“We need to be more ruthless,” said the manager, who saw Lee Vaughan sent off on the stroke of half-time.
“The two goals we conceded we poor. We knew they would counter attack us and we got done twice.
“You just can’t do that, and the second goal we have left ourselves one-on-one and we’ve played Russian Roulette.”
Flowers added on their video service: “The game changer was the red card. I didn’t think it was a straight red, I thought he was going to bring out the yellow card and I was dumbfounded when it wasn’t.
“From then we were looking to run the clock down and try and nick something at the end but the second goal killed it and from then on we’re looking not to get beat three or four.”