Match ends, Leeds United 0, Sheffield United 1.
Leeds United 0-1 Sheffield United: Chris Basham scores winner for Blades, who go second in Championship
Sheffield United boss Chris Wilder said his side must be ready for "the big push" after they climbed above Leeds and into second in the Championship with victory over their promotion rivals.
Chris Basham, playing as a makeshift midfielder, steered home the winner from 20 yards after Billy Sharp capitalised on a slip by home captain Liam Cooper to play him in.
Leeds, who dominated possession, had chances but the closest they came to scoring was when forward Tyler Roberts hit the post with a curling shot from 15 yards.
As the home side pressed for an equaliser, keeper Kiko Casilla was shown a straight red card in injury time for bringing down Sharp 25 yards from goal when he went through on the break.
"It has given us a big boost and we go into the international break full of confidence," Wilder told BBC Radio Sheffield.
"With eight games to go we've put ourselves in a great position, but this wasn't a season-defining result.
"With the ball we were pretty average but all the hallmarks of what you need to do to get a result when you're not at the top of your game were shown out there.
"After 18 months in the Championship that's probably the first time we've not been at our best but won a big game. It was a game dominated by the opposition, but we hung on in there.
"It was a true team effort. On another day the opposition probably deserved to get something out of the game, but you take any result you can get."
Defeat for Leeds gave Norwich the chance to extend their advantage at the top of the table to four points with a 2-1 victory at Rotherham United, meaning the Whites are also now five points adrift of the Canaries.
Sheffield United, who are now a point ahead of Leeds with eight games remaining after keeping a seventh successive clean sheet, had to withstand a barrage of first-half pressure as the hosts dominated.
But, although Leeds had their chances, they were unable to force Blades keeper Dean Henderson into a save as Jack Harrison volleyed over from six yards, while Roberts flashed a header wide.
The visitors grew into the game in the closing stages of the first half and improved after the break, but almost went behind when Roberts thumped the woodwork.
However, when their chance came they took it as Basham, normally a central defender, registered the game's only effort on target to secure back-to-back away wins at Elland Road for the first time since March 1961.
Leeds searched for an equaliser but Pontus Jansson, who ended the game in goal following Casilla's dismissal, poked their best chance wide from close range after being thrown up front to add nuisance value because of injury after Leeds had used all three of their substitutes.
Leeads head coach Marcelo Bielsa: "I don't want to underestimate the victory of the opponent.
"If we analyse the game, we can't be unsatisfied but we're disappointed with the result. If the opinion is that we deserved to draw, I have a different opinion on it.
"What happened today has happened many times in the past games. To explain it again after such an important loss at home with our fans, our first half hour was very good.
"We conceded the last 10 minutes of the first half but we had less quality in the second half but we dominated and we had the feeling that we were dangerous."
- 33CasillaBooked at 90mins
- 2AylingSubstituted forDallasat 77'minutes
- 43KlichSubstituted forClarkeat 77'minutes
- 22HarrisonSubstituted forDouglasat 57'minutes
- 2BaldockBooked at 18mins
- 6BashamSubstituted forLundstramat 90+2'minutes
- 10SharpBooked at 62mins
- 17McGoldrickSubstituted forDowellat 88'minutes
- David Coote
- Shots on Target
Second Half ends, Leeds United 0, Sheffield United 1.
Corner, Leeds United. Conceded by John Egan.
Corner, Sheffield United. Conceded by Kalvin Phillips.
Attempt blocked. Oliver Norwood (Sheffield United) right footed shot from outside the box is blocked.
Substitution, Sheffield United. John Lundstram replaces Chris Basham.
Kiko Casilla (Leeds United) is shown the red card.
Foul by Kiko Casilla (Leeds United).
Billy Sharp (Sheffield United) wins a free kick in the attacking half.
Pontus Jansson (Leeds United) wins a free kick in the defensive half.
Foul by Martin Cranie (Sheffield United).
Substitution, Sheffield United. Kieran Dowell replaces David McGoldrick.
Attempt blocked. Tyler Roberts (Leeds United) right footed shot from the right side of the box is blocked. Assisted by Pablo Hernández.
Attempt blocked. Stuart Dallas (Leeds United) left footed shot from the right side of the box is blocked.
Attempt missed. Pontus Jansson (Leeds United) right footed shot from the centre of the box is close, but misses to the right. Assisted by Jack Clarke.
Offside, Leeds United. Stuart Dallas tries a through ball, but Ezgjan Alioski is caught offside.
Attempt missed. Stuart Dallas (Leeds United) right footed shot from outside the box misses to the left.
Attempt blocked. Pablo Hernández (Leeds United) right footed shot from the left side of the box is blocked.
Delay over. They are ready to continue.
Delay in match Pontus Jansson (Leeds United) because of an injury.