Neil Warnock earned his first win as Leeds United manager as first-half goals from Robert Snodgrass and Luciano Becchio saw off fellow Championship play-off hopefuls Middlesbrough.
Victory failed to lift the 10th-placed visitors up the table but it may have reignited their fading top six hopes.
Rhys Williams' second-half header was the best chance for Boro, who remain fourth after a lacklustre home display.
And Barry Robson's late dismissal ended their hopes of an unlikely comeback.
Leeds now trail sixth-placed Cardiff by four points, having played at least one game more than most of their rivals.
Four wins in their last five outings had catapulted Tony Mowbray's Boro up to fourth after stumbling out of the play-off picture with a barren New Year spell of six matches without a win.
But history was not in Boro's favour ahead of the Riverside clash, having not yet beaten Leeds at home since moving from Ayresome Park in 1995.
And Boro become the architects of their own downfall, a livid Mowbray watching errors from Jason Steele and Justin Hoyte gift Leeds a two-goal advantage.
Snodgrass, made skipper by Warnock in one of his first acts since becoming Leeds boss, scored the opener, stroking home from 18 yards after being coolly picked out by a composed Aidy White's short square pass.
Darren O'Dea smashed a deep free-kick towards White in the right channel, the Leeds winger brushing off a feeble challenge from Boro left-back Joe Bennett to set up Snodgrass, whose sidefoot shot squirmed underneath Steele.
Under previous boss Simon Grayson, Leeds had no problems with their attacking incisiveness. But they had became rather toothless in front of goal in the three games since Warnock started prowling the Whites' touchline last month.
Having enjoyed the first goal of his reign, the much-travelled manager was celebrating another within 10 minutes when Hoyte's mis-kick allowed top scorer Ross McCormack to pull back and Becchio gleefully rolled home from close range.
Warnock's priority since arriving in West Yorkshire has been plugging a leaky defence, who have conceded more goals than any other top half team.
Despite their lofty position Boro hardly have a prolific strike-rate and failed to really stretch away keeper Andy Lonergan.
Midfield schemer Barry Robson was Boro's brightest spark in an otherwise dull home first-half performance and his fierce volley did stir Lonergan into punching clear.
And, seconds later, the Scot's goalbound corner was bravely headed off the line by United debutant Paul Robinson as Boro finally woke from their slumbers as the game approached the break.
Mowbray's no doubt harsh half-time words galvanised Boro as they set about Leeds with renewed purpose in the early stages of the second half.
Williams escaped his marker from a home free-kick but wastefully planted his header into Andy Lonergan's side-netting.
Boro huffed and puffed as they tried to make Leeds sweat before Robson blew his top by kicking out at Adam Clayton on 86 minutes.
He received his marching orders - ending Mowbray's hopes of salvaging an unlikely point as organised Leeds claimed a third clean sheet in four games since Warnock's arrival.
VIEW FROM THE DRESSING ROOM
Leeds boss Neil Warnock on BBC's Match of the Day:
"It's good to finally get a goal - and obviously the win.
"I thought the crowd was fantastic and it was great to get off the mark.
"I thought we played quite well in the first three games but there were some great performances out there today."