In the line-up for the first time since Boxing Day, Rashford scored a first-half brace to help Jose Mourinho's side edge past bitter rivals Liverpool 2-1 at Old Trafford.
The 20-year-old ended a run of 10 Premier League matches without a goal in front of the watching England manager Gareth Southgate and admits he was never concerned about his chances of making the World Cup squad during his spell on the sidelines.
"I didn't actually know he [Southgate] was here," Rashford told Sky Sports.
"It's nice that he's here to watch. There's a lot of players that are in contention and it's good that he's watching everyone."
When asked if he had thought much about his World Cup place, he added: "Not so much. He keeps in contact with us and lets us know where we're at so everything's straightforward and when it's simple like that it helps the player."
Rashford took his first goal with real aplomb, cutting inside Trent Alexander-Arnold and whipping a fine effort past Loris Karius.
He conceded afterwards, though, that he was lucky to carve out the opportunity for himself after a poor first touch.
"I think my first touch was actually a bad touch, I couldn't finish in my stride so I had to revive it, recover it in my second touch and the rest of it was quite simple for me," he said.
"It gives you the confidence to do more and the second one just fell to me and I put it in."