Farrell, on as a replacement, lay motionless for a worrying few moments after the illegal hit but sprang back to his feet to join the ensuing set-to and was able to play out the remaining 10 minutes of a one-sided clash.
England, despite making 10 changes, were considerably more fluent than against Tonga on Sunday, and had the try-scoring bonus point in the can by the 48th minute through the first of Joe Cokanasiga’s two tries.
They had oceans of possession to play with but unlike in Sapporo, largely managed to hold onto it on a humid night under the closed roof in front of 27,194 at the Misaki Stadium.
USA, who lost 19-year-old prop David Ainu’u to an ankle injury at the first scrum, were game but naïve and England exploited their advantage in the setpiece before picking off the minnows from there.
They were able to mothball Billy Vunipola at half time and swap both their props at the same time and if stand-in captain George Ford, bizarrely named man of the match, had not endured one of his more wasteful nights the margin of victory could have been even larger.
Ford opened England’s account in the seventh minute, spotting an inviting hole in the USA defence as Cam Dolan flew out of the line to breeze through for a try.
Two lineout drive touchdowns followed from Vunipola and then Luke Cowan-Dickie as England chose to turn down penalty shots in search of tries.
Cokanasiga should have scored the fourth before the break but after failing to capitalise on Jonathan Joseph’s break the monster wing made amends eight minutes after half time to finish what his Bath teammate started.
Opposite wing Ruaridh McConnochie slid over neatly wide out on the right for his first Test try before Lewis Ludlam earned his just desserts for a fine display with a touchdown of his own and Cokanasiga went over after a terrific run from Ellis Genge after the States were reduced to 14 men.
The consolation try in injury time from Bryce Campbell was exactly that.
Bigger challenges await in Pool C against Argentina and France but England go into them with maximum points and momentum.
England captain George Ford said: “It is a good win again. The United States were very physical and passionate.
“We will recover from this and then start the preparations from the game against Argentina.”
United States head coach Gary Gold said: “It was a very poor performance and England were very good. They are deserved winners but we weren’t very good.
“They pinned us in our own half and they did not give us an opportunity to play.
“We need to improve every aspect of our game but we cannot be missing 40% of our tackles and think we will be in the equation.”