The Sky Bet Championship leaders took the lead just after the quarter of an hour mark via a Jobe Bellingham header, with that advantage doubled through an exquisite Wilson Isidor volley in the second half.
The Black Cats were well worth the three points though, and looked a class above with their crisp passing and ability to win the ball quickly after losing it.
Des Buckingham made just the one change to the side which drew at home against Derby County in midweek, as Mark Harris returned to the starting line-up in place of the injured Siriki Dembele.
The game began with a slice of comical timing as the sprinklers on the pitch flung into action with less than 20 seconds on the clock.
Play restarted soon after again once the rogue sprinklers had been turned off, and it was the Black Cats who dominated proceedings.
Patrick Roberts jinked infield from the right-hand side and was tripped by Elliott Moore on the edge of the D, before dusting himself off to take the free kick himself, but Jamie Cumming was equal to it, diving low to his right to push the effort behind for a corner.
There was then a bit of a let off when Isidor headed off target from Trai Hume’s right-wing cross.
Two minutes later though, Bellingham found the accuracy that Isidor had lacked, when he powered in a header from another excellent delivery from right back Hume.
Midway through the first half, 19-year-old Bellingham showed his class when he waltzed around Moore and then fed Chris Rigg through the centre, with the latter denied by Cumming in the U’s goal.
United had their first sight of goal with seven minutes to go until the break when Idris El Mizouni received the ball from Tyler Goodrham on the left-hand side, but the midfielder’s effort lacked the conviction required, allowing for a simple save by Simon Moore.
Rigg then released Isidor down the centre, but Cumming provided more heroics by making a strong save at his near post to deny the powerful effort.
Buckingham made a switch at the break, as Greg Leigh came on for El Mizouni.
The change saw a tweak in formation too, as United altered to a 3-5-2 set-up with Peter Kioso and Leigh as wing backs, and Will Vaulks joined in midfield by Tyler Goodrham and Ruben Rodrigues. Harris partnered Dane Scarlett up front.
Leigh was involved nine minutes into the second period, when what seemed like a thunderous volleyed cross from the left found its way into the gloves of Moore on his goal line.
Straight at the other end, the Black Cats were inches away from a second goal of the afternoon, as Bellingham saw the angle open up for him 25 yards out, and he clipped the top of the crossbar with a great effort.
It mattered little as the home side doubled their lead less than 20 minutes into the second half, as Isidor watched a clipped Dan Neil ball fall over his shoulder before arrowing a sumptuous volley into the bottom far corner.
With just over quarter of an hour to play, Buckingham made a triple substitution as Hidde ter Avest, Josh McEachran and Louie Sibley came on for Kioso, Vaulks and Rodrigues respectively. Summer signing ter Avest was on for his debut.
Soon after, Will Goodwin replaced Scarlett for his first appearance of the campaign.
Five minutes of stoppage time were signalled, but the hosts saw out the clash with ease and comfort.
Sunderland (4-3-3): Moore; Hume, Mepham (Hjelde 88), O’Nien, Cirkin; Rigg (Browne 78), Neil, Bellingham; Roberts, Isidor (Watson 88), Mundle (Connolly 78).
Unused subs: Noukeu, Rusyn, Aouchiche, Aleksic, Johnson.
Booked: Mepham, Isidor.
Oxford United (4-3-3): Cumming; Kioso (ter Avest 74), Moore, Nelson, Brown; Rodrigues (Sibley 74), Vaulks (McEachran 74), El Mizouni (Leigh 46); Goodrham, Scarlett (Goodwin 81), Harris.
Unused subs: Ingram, Long, Dale, Ebiowei.
Booked: Scarlett, Sibley.
Referee: Oliver Langford (West Midlands)
Attendance: 40,654 (TBC away)