Barnsley's survivial hopes now hang in the balance following this Yorkshire derby defeat.
The Reds remain two points adrift of safety with a game in hand on fourth from bottom Bolton after an eighth defeat in 16 outings.
Barnsley have now won only two of their last 17 Championship matches.
They have won only one of their last eight away Championship matches and have lost four in a row for the first time since August 2017 (5)
The Reds goal in this game was an own goal, the first time they have benefited from one in the league this season (the only other occasion was against Morecambe in the EFL Cup)
Remarkably the last time Barnsley benefited from an own goal in a league game was at Elland Road last season! And again it came in a 2-1 defeat.
These two own goals - scored by Charlie Taylor and Paudie O'Connor are the only two goals Barnsley have scored at Elland Road in the last four visits, stretching back seven years.
Craig Davies in November 2011 was the last Barnsley player to score there and his winner in a 2-1 success remains Barnsley's only win at Elland Road in the last 10 visits.
Leeds have secured a league double over Barnsley for the first time since 1997-1998 when both sides were in the Premier League.
This was only Leeds third win in 20 league outings, and for Paul Heckingbottom, only his fifth in 29 games in charge of Barnsley and Leeds.
Ezgjan Alioski scored in this game and Leeds 2-0 success at Oakwell back in November, becoming the fourth player to score against Barnsley in both 2017-2018 meetings after Cardiff's Callum Paterson, Millwall's Lee Gregory and Bristol City's Famara Diedhiou.
This was the 19th game Barnsley have been level at the break this season, they have gone on to win four.
This was the 31st game in a row in which Barnsley have conceded the first goal and thus failed to win, ironically Leeds was the last opponent they have beaten having conceding first, back in January 2017 (3-2)
Incidentally since that victory which lifted the Reds up to 8th in the Championship table, they have won only 11 of 62 Championship games.
Barnsley won nine corners in the game, their most on the road this season.
Kieffer Moore (for Mahoney 62)
George Moncur (for Bradshaw 73)
Ryan Hedges (for Mills 81)
Jack Walton, Dimitri Cavare, Jason McCarthy, Ethan Pinnock.
Bailey Peacock-Farrell, Paudie O'Conner, Matthew Pennington, Pontus Jansson, Tom Pearce, Kalvin Phillips, Ronaldo Vieira, Ergjan Alioski, Samuel Saiz, Pablo Hernandez, Kemar Roofe.
Caleb Ekuban (for Alioski 71)
Adam Forshaw (for Saiz 84)
Andy Lonergan, Liam Cooper, Vurnon Anita, Pierre-Michel Lasogga, Hadi Sacko.
Leeds assistant manager Jamie Clapham said:
"The first 15, 20 minutes we were exceptional - we played really fast and were on the front foot.
"Then we got the goal and for some unknown reason we just switched off and they managed to get in the game.
"You can see the equaliser was coming for them and then at half-time we had to have strong words.
"We got the goal and controlled large periods again then. Towards the end it was a real battle and we had to man up and do everything you need to get results.
Sky Bet Championship results:
Friday 13th April 2018:
Millwall 0-3 Fulham
Sessegnon 46, McDonald 56, Mitrovic 89
Saturday 14th April 2018:
Birmingham City 2-1 Sheffield United
Roberts 32 Duffy 7
Bolton Wanderers 0-4 Wolverhampton Wanderers WOLVES ARE CHAMPIONS
Douglas 16, Afobe 45+1, Jota 53, Coady pen 66
Brentford 2-1 Queens Park Rangers
Canos 16 Sylla 45+2
Bristol City 5-5 Hull City
Pack 37 Wilson 16, 72, Fielding og 56, Hernandez 80, Campbell 87
Derby County 1-2 Middlesbrough
Nugent pen 90+2 Besic 20, Assombalonga 70
Ipswich Town 0-4 Aston Villa
Hourihane 25, Grabban 57, 78, Lansbury 82
Leeds United 2-1 BARNSLEY
Pearce 17 O'Connor og 36
Preston North End 0-0 Norwich City
Sheffield Wednesday 3-0 Reading
Sunderland 1-2 Burton Albion SUNDERLAND ARE RELEGATED
McNair 34 Bent 86, Boyce 90+2
Cardiff City 2-1 Nottingham Forest
Morrison 35 Bridcutt 50
Barnsley lie in 22nd place in the Sky Bet Championship with 38 points from 43 games.
We are 31 points outside the Play-Offs, 48 points off the Automatic Promotion Places, 60 points off First place and 2 points inside the Relegation Zone.
Up to 22/04/18
On The Road:
Sky Bet Championship Matchday Thirty Forty Four: Nottingham Forest v Barnsley, Tuesday 24th April 2018. Kick-Off: 7:45pm
Sky Bet Championship Matchday Forty Five: Barnsley v Brentford, Saturday 28th April 2018: Kick-Off 3pm.