In the five matches before the Saints had the bye in round 13, they won the first quarter only once.
That was in round 11, when they led Gold Coast by 18 points before going on to a 95-point victory.
Their first-quarter record against other opponents in that period is: West Coast (trailed by 28 points, lost by 30 points); Sydney Swans (trailed by nine, won by 18) Richmond (trailed by three, lost by eight); Adelaide (trailed by 14 points, lost by four).
"We just need to get off to better starts," Dempster said on SEN's Morning Glory program.
"Especially over the last six weeks we've been giving teams starts and then had to claw our way back in.
"If we can throw the first punch and get off to a good start that's going to really help us."
The Saints are eighth with a 6-6 record. They play North Melbourne at Etihad Stadium on Sunday evening.
Dempster admitted he worried about his spot in the team when Scott Watters was appointed coach before this season, but Watters has shown great faith in him by playing him in a new role.
Dempster, who is 191cm, has gone from tagging midfielders to playing on taller opponents in defence.
"It's something I haven't done in the past," he said.
"I'm not really that tall. Our whole backline is not that tall."
