The Cowboys appeared to be on their way to a victory after the first quarter of the game but the Broncos responded with three quick tries which could easily have been six as North Queensland opened up like a can of sardines.
The Cowboys travel to Melbourne for a Thursday night clash with their grand final opponents from 2017 and Thurston said it would be carnage unless the defensive effort was better across the park.
"With the players they have got in their team, if we defend like that, it is not going to be a good night at the office, so we have a lot to work on," Thurston said.
“When the tide turned, we needed to match them with our defence but they started running harder and blowing us apart from the ruck to all over the field."
Cowboys coach Paul Green said the start of the game, where his team dominated and led 8-nil, "probably did the side no favours" because when they were called on to defend the Cowboys allowed in cheap points and the Broncos led 18-8 at half-time
"Mentally, your team can take their foot off the gas and think ‘this is going to be easy’…and it is about lifting your defensive effort when you are asked to,” he said.
"If we had responded a bit differently in that period [before half-time], it might have been a different outcome.
"We were on top early and when that shifts the other way, you’ve got to defensively be a lot stronger than what we were."
The Cowboys could have snatched the game late but for a bizarre collision by Scott Bolton with the goalposts when he seemed certain to score.
"I hope the posts are all right," Green grinned.
"I thought Bolts was over. When you get through like that you generally score those but you can’t blame him for the loss.
"If we had defended better, we wouldn’t have been in that position to start with."