Blackett but worse was to follow a few minutes later.
Luke Shaw delivered an inviting centre from the left and Sinclair rose again to despatch another header past Gollini to turn things around. It prompted the right response from the home side as Cole strode forward to play a perfect one-two with Lingard and finish clinically with his right foot. It was a goal that would not have looked out of place at a much higher level.
After all the excitement, things dampened down somewhat until the dramatic finale. King blazed over when he had better options, including Tunnicliffe unmarked to his left, but the Norwegian made the right decision in the 89th minute when his pace took him clear on the flank. King looked up to intelligently pick out Veseli at the far post and the Swiss substitute buried a volley past Boruc for his first United goal.
Lingard almost added a fourth after being slipped through by Cole's pass as the classy pair combined again but that would have been extremely harsh on Southampton, who instead had one final roll of the dice when Chambers' speculative effort from outside the box somehow found its way past Gollini's outstretched hand and entered the net via a post.
United: Gollini; Wootton, M.Keane, Fornasier, Blackett (McGinty 67); Bebe (Veseli 78), Thorpe, Cole, Tunnicliffe, Lingard; King (James 93). Subs not used: J.Pereira, Hendrie.