The Argentina international, United’s record signing, upstaged debutant Radamel Falcao in Sunday’s game at Old Trafford with a goal, an assist and a hand in the home side’s two other goals.
He came off in the 82nd minute after suffering cramp and although Van Gaal heralded his contribution, he said that he expected the £59.7 million ($98 million, 75 million euros) winger to get even better.
“Di Maria is all right, but he has cramp. Normally you have to play 90 minutes without cramp, but that’s also a positive symbol that he gave everything,” the Dutchman told his post-match press conference.
“When you prepare three goals and you make (score) the first goal yourself, you cannot play bad. But he had a lot of unnecessary losses, so we can do better. Even Angel di Maria.
“Can you do better when you prepare three goals and make one? It’s nearly impossible. But I’m a coach and I analyse the game and I see things we have to improve as a team.”
Di Maria put United ahead in the 24th minute with a free-kick from wide on the right that crept in at the far post.
He instigated the moves that saw Ander Herrera and Wayne Rooney swell United’s lead with a pair of low strikes before half-time and then teed up Juan Mata to add a fourth goal with a mishit shot in the 58th minute.
Having seen his side go four games without winning prior to Sunday’s game, Van Gaal rejigged his line-up by introducing a four-man defence and a diamond midfield.
But despite the impressive nature of United’s performance, the former Netherlands coach said the decision to jettison his 3-4-1-2 formation had been imposed upon him by circumstance.
“I could hardly play with five defenders because (Chris) Smalling and (Phil) Jones were injured,” Van Gaal explained.
“So I was more or less forced to play with four defenders, but it’s also because of the quality of players that I changed the system.”
He added: “I said to the players before the match that we have to make a new start today.”
– Van Gaal’s championship ambition –
United, who also gave debuts to Marcos Rojo and Daley Blind, finished the game with substitute Falcao alongside Robin van Persie in attack and with Rooney operating as a number 10.
But Van Gaal dismissed suggestions that this could be the most attacking side he has ever coached.
“I’ve worked already more than 35 years and I’ve played always on the attack,” said the former Ajax, Barcelona and Bayern Munich coach.
“All my teams have scored the most of the league, so I hope at the end of this league we’ll also score the most.
“But it’s not our goal. Our goal is to be in the first three, because we have to qualify ourselves for the Champions League.
“The most important thing is the trajectory. We are building a process and we have to play in a certain style, we have to improve our qualities.
“And at the end I hope to be the manager of the champions of the Premier League. If it is not this year, then in my second or third year, but I want to give the championship to the fans.”
QPR manager Harry Redknapp, who has never picked up a point in 15 league visits to Old Trafford, said his side were short of fitness.
“One or two of my players are still trying to get their fitness,” he said.
“Leroy Fer has had two weeks away with Holland, probably standing around being used as a cone.
“Sandro ended up with cramp because he’s played one game all season. We need to get a few of them up to speed and if we do, I think we’ve got a great chance.”