United were massively disappointing in the 1-0 defeat at Bournemouth last weekend, struggling to trouble their hosts' backline.
Andreas Pereira's deflected effort and a Davy Propper own goal were decisive early on and, although Lewis Dunk pulled one back, Marcus Rashford sealed all three points just two minutes later.
But that was just the tip of the iceberg in terms of United's dominance, as Rashford went on to miss another couple of presentable chances, while James, Anthony Martial, Brandon Williams and Fred all went close in the latter stages.
"The high press paid off, that's what we have been about all season, playing with energy right from the start," James said after the game.
"We were a little bit edgy when they scored and it was good to score again on the break, but we could have scored seven or eight goals."
And on Rashford's gilt-edged chance to double his tally for the day, James added: "Marcus normally scores a lot of those goals, thankfully when he missed we were already 3-1 up."
On a day when James was celebrating his 22nd birthday, the winger put in another stellar performance to help secure all three points for his side, having been recalled to the United XI after he was rested for the midweek Europa League stroll against Partizan Belgrade.
Brighton defenders Dunk and Dan Burn were both booked for fouls on the Welsh international, who had been praised by his national team coach this week for having similar traits to former United star Cristiano Ronaldo in terms of the physical treatment he receives.
James made the switch to Old Trafford from Swansea in the summer and made an immediate impact, scoring three goals in his first four Premier League matches. And while he didn't get on the scoresheet against Graham Potter's side, he was influential in helping the club climb to seventh in the table.