Saints dominated up front throughout a scrappy encounter, and that was particularly impressive as four players were making their first Franklin's Gardens starts in the green, black and gold.
Roger Wilson, Christian Day, Neil Best and Ignacio Fernandez Lobbe were the new men who beefed up and added mobility to the Saints pack, who were better than their Australian counterparts in all aspects of the game.
"We were very pleased with the forwards, and the scrum in particular went very well," said Mallinder. "To get a penalty try was pleasing."
Second-rower Day has played at the Gardens as an opposition player before, but he admitted it was much better lining up as a home player.
"It was my first taste of playing here in a Saints shirt and it was a good start," said the former Sale and Stade Francais player.
"I have played at Northampton before and I have always enjoyed the atmosphere, and it was even better on Saturday having a green shirt on rather than a blue one!"
As well as the penalty try which came midway through the second half, Saints scored two further tries through winger Chris Ashton in stoppage time, with skipper Bruce Reihana kicking a penalty and two conversions.