Sheffield United gifted arch-rivals Leeds the win which sent the visitors to the top of the Championship table.
With only eight minutes of normal time remaining, and the contest edging towards a draw, goalkeeper Dean Henderson compounded an earlier mistake by John Egan which presented Pablo Hernandez with the opportunity to score.
Henderson was put on the back foot by his defender's poor back pass but, rather than simply clearing the ball, he tried to pass it out from the back. That handed Leeds possession and allowed Hernandez to slide home into an empty net.
Conor Washington hit the crossbar as United went in search of an equaliser but the visitors lead remained intact.
Dean Henderson 6
Had little to do until the ball fell for substitute Aapo Halme following Barry Douglas' set-piece. But, as all good goalkeepers do, he kept his concentration to make a fine reaction save; scrambling the ball to safety. Also produced some important but comfortably blocks as Leeds improved after the interval but undid all his earlier good work to gift Leeds the win.
Jack O'Connell 6
Once again, went about his work with the bare minimum of fuss and provided rock solid support for defensive colleagues John Egan and Chris Basham. Brought a real physical presence to United's rearguard. Did not catch the eye like Basham, but was effective in his own way.
John Egan 6
Did exactly what he does every game; plays simple, effective football. The Republic of Ireland international also demonstrated good positional sense by making some important interceptions when Leeds broke forward on the counter attack. Kemar Roofe caused him some problems, though, and he was booked. Set in motion the chain of events which led to Hernandez's goal.
Chris Basham 8
Plays centre-half possibly like no other centre-half in the Championship. Bielsa is a master tactician but his players struggled to fathom how best to cope with Basham's driving runs from deep lying positions. Probably because many of them have not faced anything like it before.
George Baldock 6
Making his first appearance since the beginning of last month and first start since September, the wing-back seemed to get up to speed well but will clearly take a couple more matches to truly find his rhythm.
Enda Stevens 7
Like his compatriot and international team mate Egan, Stevens was cautioned for a foul before the break. Unlike the caution his colleague received, though, his appeared harsh. He escaped a second after catching Stuart Dallas in front of the dug-outs just before half-time although, in fairness to Bielsa and his staff, none of them appealed for a booking. Made a crucial defensive header during the closing stages, having gone close at the other end on the hour.
Oliver Norwood 6
Kept things ticking over in midfield, even when Leeds managed to set themselves behind the ball, by constantly shifting the direction of play. But that area of the pitch was so crowded, with both teams looking to press whenever they lost possession, it proved difficult for Norwood to really influence the game.
John Fleck 6
Produced a moment of brilliance just before half-time, losing his marker with a drop of the shoulder and feint before being crowded out. The midfielder was not United's stand-out performer but his work ethic and tenacity were important in the battle for supremacy.
Mark Duffy 7
Sometimes drifted in front of his strikers and sometimes operated just behind the front two. With Leeds leaving little space between their defence and midfield, this game was all about intelligence rather than industry for Duffy. Showed plenty when he led their midfielder and defenders a merry dance before producing a chance for David McGoldrick.
Billy Sharp 6
His first sight of goal came midway through the first period, after his good friend Liam Cooper had departed injured for Leeds. On that occasion, with the ball flying inches behind him, Sharp failed to get a shot on target. Another came, just before half-time but his stooping header bounced over the crossbar.
David McGoldrick 7
Douglas was forced to make a good interception to deny the centre-forward a shot on goal during the early exchanges before Bailey Peacock-Farrell turned his low drive around the post soon after. Even during quiet periods, McGoldrick always makes defenders work with his movement off the ball and worked hard to support his defence too. But his finishing still leaves a little to be desired.
Substitutes: Conor Washington (Duffy 63), Marvin Johnson (Stevens, 84).
Not used: Moore, Coutts, Lundstram, Stearman, Cranie.