Two-nil down at halftime at St Mary's, Solskjaer threw on Cavani for the start of the second-half.
Cavani immediately had an impact, laying on a superb cross for Bruno Fernandes to pull one goal back.
From there, United kept knocking on the door and eventually Cavani was able to draw level with one trademark header. Then in injury-time, the Uruguayan reacted to Marcus Rashford's cross to fire another header past Saints goalkeeper.
Solskjaer was delighted with his super-sub's performance as United won 3-1 on the south coast and was effusive in his praise for Cavani afterwards: