The Argentine particularly impressive and settled any early United nerves when his free-kick delivery crept into the far corner.
Ander Herrera drilled in soon after and Wayne Rooney’s sharp finish all but ended the contest before the break.
Juan Mata steered in Di Maria’s shot and loanee Radamel Falcao had a gentle debut as a 67th-minute substitute.
Tougher tests than a flimsy QPR side await, but after a dismal season under David Moyes, and a slow start to this campaign under successor Louis van Gaal, United provided its fans with genuine cause for optimism.
United’s last home game – a 2-1 opening-day defeat to Swansea – had finished with a very different mood around Old Trafford and Van Gaal’s starting line-up showed major changes from that loss.
New signings Di Maria, Daley Blind and Marcos Rojo were included from the start with Falcao on the bench.
As well as new personnel, Van Gaal was forced to shift from his favoured 3-5-2 formation to a four-man defence by injuries to Chris Smalling and Phil Jones.
The changes fuelled a buoyant atmosphere among the home fans and QPR proved the perfect opposition for a confidence-building win.
Mata, playing at the attacking tip of a midfield diamond, shot over from 20 yards, before Di Maria gave United a goal cushion to go with the majority of possession.
The £59.7m signing’s free-kick floated over its intended targets and, with goalkeeper Rob Green stood still in expectation of a touch, bounced inside the far post.
The visitors had rarely ventured beyond the halfway line, but if Jonny Evans had not blocked Matt Phillips’s shot after David de Gea rushed out to try and halt a rare attack, they could have been level.
As it was, QPR was out of the game soon after.
A scampering run from the increasingly impressive Di Maria drew the attention of two defenders and when Wayne Rooney laid the ball into the path of Herrera, the Spaniard drilled a low shot into the bottom corner.
The third arrived soon after as the QPR defence stood off its men, allowing Mata and Herrera to exchange passes and Rooney the time to pick his spot inside the near post.
The introduction of Armand Traore improved QPR after the break, but Mata and Rooney’s over-elaboration with the goal at their mercy, and the rueful smiles that followed, summed up the exhibition pace of the second half.
Mata did not have to wait long for another chance – blasting home after Di Maria shanked an ambitious effort into his path.
Falcao was introduced to loud cheers with a little over 20 minutes to go and was only denied a goal by Green’s scrambling recovery save.
The Colombian’s new side should provide him with plenty more chances if they continue in the same vein, while QPR will need to be more determined and ambitious to survive in the top flight.