The £10million summer signing from Manchester City capitalised on woeful defending to head home Sebastian Larsson's corner on the half-hour, in the process cancelling out Juan Mata's opener.
But in truth, the Spaniard's 17th-minute strike had come against the run of play with the visitors once again misfiring alarmingly as they tried to come to terms with Van Gaal's 3-5-2 formation.
Even Robin van Persie's presence could not spark a marked improvement on a day when reports claimed Real Madrid striker Angel di Maria was heading for Old Trafford, and the Black Cats, roared on by a crowd of 43,217 at the Stadium of Light, gave as good as they got.
United lacked both invention and penetration as Sunderland head coach Gus Poyet looked to exploit their frailty at the back by asking Connor Wickham and Will Buckley to utilise the space behind Ashley Young and Antonio Valencia, which they did to good effect.
Buoyed by Van Persie's return, United emerged looking for a significant improvement on their performance in last weekend's home defeat by Swansea.
However, what Van Gaal got was a display every bit as dysfunctional as the one which heralded the start of the new campaign.
His decision to field Young and Valencia as wing-backs once again exposed a fragile back three of Phil Jones, Chris Smalling and Tyler Blackett which was further reduced in terms of experience when Smalling limped off before the break to be replaced by Michael Keane.
But it was not only at the back that the visitors struggled with Sunderland clearly carrying the momentum of last season's two victories over United, and skipper Wayne Rooney and strike-partner Van Persie saw little of the ball where it mattered most.
Nevertheless, it was United who took the lead, although they did so at a time when the breakthrough looked more likely to come at the other end.
Young had already put his defence under pressure with an aimless cross-field pass and Lee Cattermole unleashed two long-range efforts when winger Buckley, making his full debut for the Black Cats, cut inside Blackett and crossed for Wickham, who wastefully scuffed his shot straight at keeper David de Gea.
Sunderland were made to pay within seconds as Valencia managed to ease past full-back Patrick van Aanholt and cross low to the far post, where Mata ran off the back of Larsson to score from close range.
The goal visibly settled United and they enjoyed a sustained period of possession as they threatened to take control.
However, they allowed their hosts back into the game on the half-hour when, after Buckley's direct play had earned his side a corner, Larsson delivered the resulting set-piece to the near post and Rodwell headed firmly home with Valencia having done little to impede his progress.
United's response was lukewarm, and there was little doubt that Poyet would have been the happier of the two managers as their respective teams left the pitch at the break.
Indeed, the home side might have taken the lead six minutes after the restart when Wickham was given time to work himself into a shooting position inside the box and Blackett somehow blocked his effort with De Gea beaten.
But Van Gaal's men gradually assumed control as they dominated possession, although with Sunderland defending deep, space was at a premium even with Rooney dropping ever deeper.
They almost found a way through with 62 minutes gone when Van Persie surged into the box only to be halted by Vergini's last-ditch challenge, and Young was booked for simulation after going over Wes Brown's leg as the pair closed on the rebound.
Van Persie departed seconds later as he and Darren Fletcher were replaced by Danny Welbeck and Adnan Januzaj, but Larsson failed to make the most of Wickham's fine 68th-minute through-ball as United lived dangerously once again.
Larsson passed up a good opportunity when he curled a free-kick well wide with 15 minutes remaining with Sunderland hunting all three points.
To that end, Poyet attempted to pile the pressure on the visitors' rearguard with the introduction of battering-ram frontman Jozy Altidore, although defensive confusion inside the Sunderland penalty area very nearly cost them on more than one occasion in a frenetic finish.
Source : PA
Source: PA