Both attackers scored in the 4-0 rout.
Rashford said, "I said to him 'once you get the first goal, the rest will come naturally'.
"That goal is nothing but instinct. You can tell he's a natural finisher, that's what he's best at.
"So for him, he doesn't have to change anything, he'll come into the team, do his stuff and he'll score goals and that's what he does."
Rashford was asked about United's pressing game, which has been a feature of their pre-season matches so far and added: "I think there's a lot to improve on still, but for us it's about getting the pictures in our heads.
"It's been a while since we've been a real pressing team, but now we've laid down the fundamentals of how we actually want to press.
"I think now as time goes on we'll improve and get better."