Manchester United manager Jose Mourinho saw his side’s performance level drop in the second-half, but was largely happy with the display.
In an opening 45 minutes dominated by the Red Devils, their first goal came after just 13 minutes as Ashley Young completed a solo goal which sent the Old Trafford crowd wild.
Juan Mata soon made it 2-0 before Romelu Lukaku sent United into the break 3-0 ahead.
Fulham grew into it after the break and pulled one back from an Aboubakar Kamara penalty, before an Andre-Frank Zambo Anguissa red card put United back in control, with Rashford netting the final goal.
Mourinho was pleased with the overall performance, but acknowledged Ranieri’s tactical changes that altered the game.
Speaking to Sky Sports he said: “The first half was really good. We gave no chances to Fulham. We were strong, aggressive and intense. At times it was beautiful football. The first half was perfect.
“The second half was Ranieri’s fault. He made two changes that improved his team and gave us problems that we didn’t have in the first half. I also think there was some fatigue in some of my players. A few factors made the second half not as good as the first.
“We were intense without the ball and with the ball. Without the ball we pressed, we kept Mitrovic away from the goal. With the ball it was simple, one or two touches. We were really good.
“We needed it. The last three matches we didn’t lose, but didn’t win. Now we have two away matches, then two at home. Let’s see if we can get more points from those matches.
“The players have shown they can be a better team than they are. When there is solidarity in the team, everyone giving their maximum, you attract more positive things.”