Marcus Rashford (2), Antony (pen), Alejandro Garnacho (2) and Christian Eriksen (2) struck for United to mark their biggest win under Ten Hag.
The manager later said: “First of all, it was a difficult start but, once we found the shape, it’s not so weird because it’s the first time this team is playing together.
"But once we found the shape and the patterns, we scored some great goals, starting with Rashford which was a brilliant goal but I’d also say some other goals were really good. We played with a lot of speed and we were very ruthless in front of the goal.
“The key was finding the shape and, of course, the right attitude. We were 100 per cent concentrated and we certainly played very good. I think it was enjoyable to watch and also the fans they liked it and appreciated it. You could feel again the good bond between the team and the fans and we gave the fans some nice goals.”
On Manuel Ugarte's full debut, he added: “I think he was good. Also for him, in the first minutes, you have to find your position and, as a team, you have to find the right shape. Once we got it, then you see his level and he can really strengthen the squad and the team.”