Wayne Rooney scored twice, Danny Welbeck found the net with a stunning goal, Ashley Young bagged a brace and there was also a double for 20-year-old left-back James as United strolled to victory at the Rose Bowl
United dominated the match from start to finish and they fully deserved the comprehensive win, which came in front of a crowd of 86,432.
Winning the Chevrolet Cup will not rank high on Van Gaal's list of achievements when he retires, but the Dutchman will at least be happy in the knowledge that his reign as United boss started off very well.
Twenty-four hours earlier Van Gaal had complained about his team being dragged across the United States on their pre-season tour, but he sported a big smile after the final whistle.
United played with a high-tempo, their work-rate was impressive despite the intense California heat, and their finishing was clinical.
Ander Herrera was the driving force behind United's success in the first half, spraying probing passes from deep and Welbeck showed just how destructive he can be in behind the opposition defence.
Another big plus for Van Gaal was the way his defence performed
Lining up in the 3-5-2 formation he used at the World Cup with Holland, the spotlight was on Chris Smalling, Jonny Evans and Phil Jones
They all passed the test with flying colours.
Tougher tasks will come for Van Gaal, but the difference between Wednesday's hammering and the 1-0 defeat David Moyes suffered against the Singha All Stars in his first game in charge, could not be bigger.
He may not have scored, but the star of the night was Herrera.
The £28million signing made an immediate impact, collecting the ball from Juan Mata before letting fly with a 25-yard shot which Jaime Penedo did well to turn over.
Welbeck then beat the Panamanian with a top-drawer finish from 25 yards
Mata was the architect
He intercepted a Galaxy pass and then nudged a pass to the striker, who swung his right foot through the ball and it flew in off a post
United were dominating and the under-scrutiny back three never looked like conceding.
The only time the Galaxy pierced the United defence, Jones put in a last-gasp challenge to deny Robbie Keane.
The first of two defensive errors allowed United to double their lead three minutes before half-time.
AJ Delagarza stretched out his right arm to meet Antonio Valencia's cross and Referee Baldomero Toledo had no choice but to award a penalty.
Rooney slotted the ball past Penedo and in injury time he made it 3-0 with one of the easiest goals he will ever score.
Tommy Meyer let Valencia's tame cross run through his legs
Rooney was unmarked in the centre and he prodded the ball past Penedo at the second attempt.
Van Gaal made nine changes at the break
Darren Fletcher, captain ahead of Rooney, and Herrera were the only two survivors.
Fletcher dropped to centre-half and Herrera was pushed up field just behind Nani and Young, who led the United attack.
United's new-look line-up took a few minutes to adjust, but they soon managed to add to their tally.
Young spotted James at the back end of the box and he drilled a low shot past Penedo before being mobbed by his team-mates.
The youngster added his second six minutes from time when Penedo spilled Young's shot and he swept the ball into an empty net.
Young made it 6-0 by rounding Penedo and slotting the ball home following a slide-rule pass from the impressive Herrera.
And the former Aston Villa winger then converted Rafael's pass in the dying minutes to complete the rout.
Source : PA
Source: PA