After this stroll of a victory José Mourinho became the latest Manchester United manager to rule out a move for Real Madrid’s Cristiano Ronaldo.

“Mission impossible” was how the Portuguese billed it. “We have never thought about it because he is such an important player for his club, of great economic power. I am not a defender of my club once you waste time on players who are mission impossible,” he said, and so United fans will have to put on hold their dreams of a romantic return of a player they still adore.

Of Real’s Álvaro Morata, who Mourinho has targeted, the manager said: “It is a question for Florentino [Pérez, Real president]. He belongs to Madrid. Madrid has decided and we have not come to an agreement. It is simple. It is a shame. It is a player who made it to the first team with me [when he managed Real]. We have a special liking for [him], he is someone special. I enjoyed watching his evolution in Juventus and Madrid. It is like that. I don’t think he can end with us.”

United’s post-Wayne Rooney era began with Mourinho fielding a rarely deployed 3-5-1-1 and the £75m man Romelu Lukaku waiting until the second half for his debut.

United’s new No9 did not score yet did not appear out of place against a particularly poor LA Galaxy outfit. Mourinho said: “A good thing for me today is he [showed] he’s a team player and was not worried about himself. He was worried about the improvement of the team. He didn’t score goals, but he played better than the ones who did score goals.”

Mourinho confirmed the three centre-backs shape is not next term’s default formation but will be deployed occasionally, and said there is no official deputy to the new captain, Michael Carrick.

“We don’t have a vice captain, a captain is enough, Michael is obviously the captain,” he said. “I don’t like the criteria that the captain is to be the one with the most time in the club because sometimes you have somebody with the armband just because he arrived before other players. We are going to try and feel, and make decisions, we have people that step by step we have to prepare because Michael will be the captain for one year, maybe two if he decides to do that and his body resists the demands of the Premier League and Champions League. But for the season only one captain.”

In front of a watching David Beckham, who gave this friendly a touch of glitter, United’s first outing since Rooney left for Everton and the Europa League was claimed in late-May began perfectly.

Captained by Carrick, less than three minutes were gone when United shifted gear. Jesse Lingard, the left wing-back, forced the ball into Marcus Rashford’s path. Rashford cantered forward and rolled beyond Jon Kempin, and that was 1-0.

Marcus Rashford, left, scored in the third minute to set Manchester United on their way. Photograph: Harry How/Getty Images

These pre-season affairs often feature mistakes caused by ring-rust. Marouane Fellaini offered an illustration following Rashford’s opener. The midfielder’s errant touch handed the ball to Bradford Jamieson IV and United were lucky to escape.

Juan Mata performed a sweet pivot-and-shot that Kempin saved well to his left and this was about all the action until Rashford doubled his tally and United’s lead.

Ander Herrera pick-pocketed possession and played the ball to Mata. He recycled this on to the 19-year-old and the finish, from the right, was accomplished.

Three years ago United’s Louis van Gaal vintage gave Galaxy a 7-0 smacking in Pasadena. When Fellaini banged a left-foot strike in from a clever Lingard cut-back it was 3-0 and the MLS franchise were staring at a similar trouncing.

The lead was a cushion that allowed United to relax and ping the ball about. This gave Galaxy the run around and will have pleased Mourinho.

The United manager kept his word and fielded a completely different XI for the second half. It meant Lukaku was on for Rashford and Victor Lindelöf, the other new signing, made his United bow, too.

Moments after kick-off Lukaku missed a gilded chance to open his account for the club. Pogba pushed the ball to him but when he swivelled-then-shot Brian Rowe, on for Kempin, saved. Lukaku’s next contribution was better. A deft pass fed Henrikh Mkhitaryan but the Armenian failed to finish.

This is to be a fascinating upcoming campaign for Anthony Martial. The Frenchman dazzled two years ago and faded last season. He frustrates Mourinho as the Portuguese sees a player with a high-end talent who struggles to harness it consistently. The way Martial roved forward just before the hour and caressed a 35-yard effort that went close and hit the roof of Rowe’s net signalled his quality.

Mkhitaryan’s goal – on 66 minutes – oozed class, too. United attacked at will, and during this foray, Martial ran at the Galaxy defence, switched the ball inside, and the Armenian did the rest.

Within five minutes Martial netted courtesy of a slick Timothy Fosu-Mensah cut-back and that was 5-0. Towards the close Giovanni dos Santos scored for Galaxy after he left Lindelöf a statue. The same player scored minutes later and once more Lindelöf was at fault. The Swede failed to challenge at a corner, Dave Romney headed forward, and Axel Tuanzebe allowed Dos Santos to deflect the ball in.

Mourinho will not be happy at the sloppy end. But, overall, this was an apt opening to the tour for his side.

LA Galaxy (4-5-1): Kempin (Rowe, ht); Smith (Van Damme, ht), Steres (Romney, ht), Arellano, Diallo (Cole, ht); Garcia (Jones, 60), Villarreal, Jamieson IV, Mendioa, Lassiter (Alessandrini, 60); McInerney (McBean, ht)

Subs from: Van Anholt, Pedro, Dos Santos, Boateng

Manchester United (3-5-1-1): De Gea (Pereira J, ht); Jones (Bailly, ht), Smalling (Lindelöf, ht), Blind (Tuanzebe, ht); Valencia (Fosu-Mensah, ht (Mitchell, 85)), Carrick (Pogba, ht), Herrera (Pereira A, ht), Fellaini (Mkhitaryan, ht), Lingard (Darmian, ht); Mata (Martial, ht); Rashford (Lukaku, ht)

Subs not used: Romero, McTominay

Referee: Kevin Stott

Attendance: 25,667