Sir Alex obviously felt it was time to introduce a calm head, replacing Smalling with Rio Ferdinand, in an attempt to steady the ship. At least Rooney mustered a first noteworthy effort of the second half on 71 minutes but his shot lacked the power to beat Boruc after being picked out by strike-partner van Persie.
Nani joined another substitute, Rafael, on the field with Jones reverting to midfield as United desperately sought to regain some energy and sparkle. Nani was quickly involved with van Persie unable to convert his cross due to a brilliant stop by Boruc and, when the Dutchman did find the net from a Rooney centre soon afterwards, he was flagged offside.
It looked a marginal decision but Pochettino's men retaliated to earn a free-kick at the other end which allowed De Gea to show off his quality, diving to claw away Lambert's effort in spectacular fashion. Rooney over-ran the ball from a van Persie flick, which enabled Boruc to save at his feet, but the Reds were at least showing more menace as the match entered its closing stages.
Yet the lead remained a slender one with Vidic needing to block Lambert's drive and Schneiderlin popping a drive too high seconds later. When the fourth official showed three minutes of additional time, it was at a time when there was one-way traffic from Southampton. United managed to hold on for three points but it became all hands on deck at the death with two-goal Rooney required to defend desperately.