Senior coach Ross Lyon coached the Saints from 2007 until joining Freo at the end of last season, but Duffield says the only focus for his side was the task at hand on Friday.
"We're going to work hard on not letting outside influences distract us from the performance itself," Duffield said.
"We're focusing on how we want to play football and how we want to go about the game.
"We believe if we do that to the best of our ability, we'll be right in the game."
Duffield said Lyon's knowledge of St Kilda would be utilised to a point, but Freo wouldn't be hanging their hats on that getting them over the line.
"Ross was their senior coach for a long period of time and he probably knows them better than anyone, so I'm sure he'll feed through the information we need come game day," he said.
"But we're focussing on how we want to play."
Duffield said it was pleasing to win both games at home so far this season, but the team had to begin improving its away form if it wanted to be a legitimate contender.
"We haven't been very good on the road in Melbourne, so that's something that we're focusing on," he said.
But the 27-year-old was confident all the hard work the players had done over the pre-season would hold them in good stead, both home and away.
"We've worked hard on fitness, and all the guys are versatile and playing some different roles, which is very important," he said.
"We'll go into the game with confidence in the work that we've done and hopefully come away with a good result."
