Torquay United manager Chris Hargreaves admitted goalkeeper Michael Poke's mistake had been the turning point in a 3-1 loss that saw Chesterfield stay three points clear at the top of Sky Bet League 2.
Hargreaves's team looked in control and on course for a vital win after Shamir Goodwin raced clear down the right in the 50th minute to fire an unstoppable shot into the roof of the net from 15 yards.
Chesterfield were finding it hard to break down an organised Torquay side but six minutes later Poke's attempted clearance hit Krystian Pearce in the back and Eoin Doyle ran through to equalise.
Torquay should have regained the lead after Goodwin hit a post in the 78th minute but substitute Conor Wilkinson put the rebound wide and two minutes later, Liam Cooper put Jay O'Shea in to score from the edge of the box.
O'Shea added another in stoppage time but Hargreaves knew the damage had already been done.
"We contained a really good side and scored a fantastic goal but we made some decisions that have cost us and conceded a goal at a time we were comfortable," he said.
"Let's just say it was an unusual goal to concede. We've given them a goal which is hard to take because it's hard enough to score goals and we've scored a fantastic one and they've scored an awful one.
"It was a pivotal moment but Pokey has been great for this club and he's made a mistake that we are disappointed with but it's something he's probably not done before and will never do again.
"It's frustrating because it's hard to score a goal in football but that's life, we all make errors and we have to dust ourselves off and recover quickly because there's no point in laying on the floor because no one cares about Torquay United apart from us."
Chesterfield manager Paul Cook knew his team had not been at their best.
"We never played well in the first half, we never got going, we were flat," he said. "Certainly we were painful for a long, long period of the game but the players deserve great credit for getting a win that didn't look like happening.
"Torquay scoring gave us a little bit of a rocket but we have got such good players who can make an impact on the game and it's going well for us at the minute and the players should take all the plaudits."
O'Shea showed the strength in depth Cook can call on with an outstanding performance.
"I have great faith in Jay O'Shea and my job as manager is to make sure I give all these lads minutes on the pitch," he said.
"Jay showed exactly what he is about, not that we doubted him or didn't know, and that's what I've said to people that we have goals in the team, we got three and we seem to score regularly. Torquay deserve credit for stifling us for a long time and making it difficult but in the end it was a really good win."