The Hammers’ record signing blasted home only his second top-flight goal of the season shortly before the hour mark to seal a first victory at Bramall Lane for 52 years.
As well as continuing West Ham’s encouraging form, the result ensured that winless Sheffield United have still picked up just one point - from nine matches - in 2020/21 as they continue to struggle badly in their second campaign back at the top level.
West Ham were unchanged from their dramatic late win over Fulham before the international break, with David Moyes opting not to risk Michail Antonio despite the influential forward returning to training after a hamstring injury.
Meanwhile, Sheffield United showed three changes from their 4-1 drubbing at Chelsea, with Oli McBurnie handed a recall up front and Rhian Brewster on the bench as the injured Enda Stevens and John Lundstram were replaced by Chelsea loanee Ethan Ampadu and the fit-again John Fleck respectively.
The Blades started the contest in positive fashion, with George Baldock forcing an early save from Lukasz Fabianski after the full-back got in behind Arthur Masuaku to connect with John Egan’s long pass.
After a couple of early scares, West Ham quickly grew into the game and began to dominate proceedings, with Jarrod Bowen seeing a shot blocked before Sheffield United raced forward on the counter-attack and Fabianski was called into action again to deny McBurnie and Fleck.
Aaron Ramsdale later kept out a low drive from Vladimir Coufal and West Ham should have gone ahead when Pablo Fornals’ cross from the left was flicked high over the defence by Haller, only for Tomas Soucek to fluff his lines from close range.
The first half ended in frantic fashion, with McBurnie’s header parried over the crossbar by Fabianski and McGoldrick’s flick bouncing back off the post before Bowen beat Ampadu after being released by Fornals.
His disappointing shot was blocked by Egan and a competitive opening 45 minutes finished goalless.
After the interval, only good work from Ampadu prevented Haller from finishing off a clever lofted ball from Declan Rice, but the newly-declared Ivory Coast international was soon celebrating.
After a long clearance from Ramsdale, Coufal launched a swift West Ham counter-attack and Bowen and Fornals linked up nicely before the latter had a shot blocked.
The ball then fell kindly for Haller, who rifled home a powerful drive from the edge of the box. Ramsdale got a hand to it, but couldn’t hope to repel such a fierce strike.
Sheffield United lost Ampadu to injury shortly afterwards and Angelo Ogbonna - himself back after shaking off a groin problem - headed a free-kick over before Rice saw a deflected shot held and McGoldrick fired over from distance.
Haller spurned a glorious opportunity to double his tally and put the game firmly to bed when he tapped Masuaku’s low cross wide, while the imperious Rice - fresh off scoring his first England goal against Iceland in midweek - and busy McBurnie both rattled the woodwork in quick succession.
The Blades threw everything forward in the final stages, but couldn’t find the goal that would have brought only their second point of a dismal season to date.