Two games, two defeats and five goals conceded is not how it was supposed to be for a Blades side expecting to be firmly in the hunt for promotion.
Slipping to a joint-heaviest defeat since Chris Wilder’s return to Bramall Lane a couple of summers ago was bad enough.
But it was the manner in which a defence bolstered this summer by the arrival of club record signing John Egan was so easily picked apart in the first half that made the journey home down the A19 for the 998 travelling fans such a worrying one.
Sure, Boro – like Swansea City, United’s conquerors on the opening day – are among the best the Championship has to offer.
The problem last night, however, was that Tony Pulis’s side cruised to all three points without having to get out of second gear in a clash brought forward by the Football League to accommodate Boro hosting West Bromwich Albion in front of the Sky cameras on August 24.
Two goals of the three-goal salvo that left the Blades reeling inside 25 minutes came from corners, Martin Braithwaite and Aden Flint the grateful beneficiaries of some woeful marking.
Stewart Downing added the third and the United backline was equally statuesque as the former England international was allowed to ghost between two defenders before applying the final touch.
No wonder Wilder bore the look of a distinctly unhappy manager on the touchline, his mood hardly lifted by the second-half rally that followed Ben Woodburn’s introduction from the bench.
As for Middlesbrough this was quite an end to a week that has seen the Teesside coffers swelled to the tune of £40m thanks to Adama Traore following Patrick Bamford and Ben Gibson out the door to join Wolverhampton Wanderers.
Tony Pulis is keen to spend at least some of that cash bounty before tomorrow’s deadline, but on this evidence Boro may already be well equipped to make a sustained challenge.
Braithwaite was excellent, as was Adam Clayton in midfield alongside former Leeds United team-mate Jonny Howson.
Lewis Wing, making his first start, also looks a real find. Plying his trade in the Northern League with Shildon as recently as a little over a year ago, the 23-year-old seemed perfectly at home in the second tier.
Not only was Wing lively throughout, but his delivery from set-pieces could make him an integral part of Pulis’s side.
The home fans clearly agreed, Wing afforded a standing ovation from the 22,960 crowd when substituted eight minutes from time.
It was well deserved, not least because his first two corners had brought goals.
Just seven minutes had been played when Wing’s corner found Braithwaite via the slightest of flicks from Dael Fry.
The Boro forward, fresh from sparking the late fightback that rescued a point at Millwall on Saturday, duly made no mistake from close range.
Wing’s second corner was, if anything, even better. Flint was the beneficiary of the wideman’s pinpoint accuracy this time, the £8m summer signing from Bristol City left with the simple task of heading past Dean Henderson.
Nineteen minutes were on the clock as Flint wheeled away in celebration and it was not long before United’s night took another turn for the worse.
Again an inability to deal with a ball from the flanks was the visitors’ undoing. Ryan Shotton this time provided the cross as Downing nipped between the statuesque George Baldock and John Fleck to score.
The game effectively over with 65 minutes still on the clock, frustration got the better of United for a time.
Both Leon Clarke and Chris Basham were fortunate to escape with a booking apiece for lunges that, with a less lenient referee than Robert Jones, could have brought stiffer punishments.
Eventually, though, United did start to play again. Woodburn found Clarke, but his header bounced just wide of a post.
Lee Evans, scorer of a memorable double against Middlesbrough last season in a 2-1 win at Bramall Lane, then had a couple of efforts that flew wide before Clarke was denied by a fine Darren Randolph save.
Stevens was the next to test the Republic of Ireland international’s reflexes, but again Randolph was equal to an effort that he beat away with two hands.
It means United’s sorry record of not having scored at the Riverside since 2007, a run that now stretches to five games, was maintained. A big response is needed when Wilder takes his side to Queens Park Rangers this weekend.
Middlesbrough: Randolph; Shotton, Flint, Fry, Friend; Howson (McNair 71), Clayton, Downing, Wing (Leadbitter 82); Assombalonga (Fletcher 78), Braithwaite. Unused substitutes: Dimi, Fletcher, Johnson, Chapman, Tavernier.
Sheffield United: Henderson; Basham, Egan, O’Connell; Baldock, Fleck, Lundstram (Woodburn 46), Evans (Leonard 82), Stevens; Clarke, McGoldrick (Duffy. 69). Unused substitutes: Moore, Sharp, Leonard, Stearman, Bryan.
Referee: R Jones (Chester).