Okafor punished United’s sloppy defending with a brace in the first-half before Lisandro Martinez was sent off after pulling Dominic Calvert-Lewin’s hair after the interval.
Casemiro got one back for United, but Leeds held on for their first win against United since a shock 2010 FA Cup success when they were in the third tier.
The Yorkshire club were able to celebrate their first top-flight win against United since 2002 and their first league victory at Old Trafford in 45 years.
A first win in seven league matches lifted Daniel Farke’s side six points clear of the relegation zone, with six games left to preserve their top-flight status after last season’s promotion.
As well as battling for survival, Leeds are through to the FA Cup semi-finals, where they face Chelsea at Wembley on April 26.
While Manchester City and Liverpool are United’s main rivals, their fans’ enmity with Leeds supporters goes back decades, featuring numerous clashes between hooligan gangs.
That made the defeat a bitter pill to swallow for United fans, who booed Michael Carrick’s side at full-time.
It was only Carrick’s second defeat in 11 games since he replaced the sacked Ruben Amorim as interim boss in January.
United remain in third place, seven points ahead of sixth-placed Chelsea in the race to qualify for the Champions League via a top-five finish.
The last time United played Leeds, Carrick was on holiday with former Old Trafford team-mate Wayne Rooney and their respective families in Barbados.
Carrick has revitalised United since taking charge, but one win from their last four games is a step back.
United’s trip to Chelsea on Saturday offers another chance to take a step towards returning to Europe’s elite club competition for the first time since 2023-24. (AFP)
