Ole Gunnar Solskjaer's men went into the contest in fine form but struggled to control proceedings against the tenacious Saints, who levelled in the sixth minute of additional time. 

A busy start from Southampton led to the visitor taking an early lead through Stuart Armstrong but United hit back, Anthony Martial teeing up Marcus Rashford for the equaliser before scoring his 50th Premier League goal to put the host in front. 

United had chances to increase the lead but failed to take them, and Obafemi scored from close range in the 90th-minute, leaving the Red Devils fifth in the table. 

The Red Devils' destiny in the Champions League remains in their own hands - with a visit to fourth-placed Leicester City on the final day of the season - but this result is a major blow for Solskjaer.