The arch-rivals were locked at a goal apiece in their Premier League clash when Jürgen Klopp sent on his No.23, who scored the first of his crucial double 144 seconds later.
Shaqiri then added a third to put the game beyond United, a result which lifted the Reds back to the top of the table and extended their unbeaten start to 17 matches.
And, speaking to Liverpoolfc.com after the final whistle, the Switzerland international explained how he used his natural disappointment with being a substitute as motivation to influence the outcome when he got a chance.
“Every player is not happy when he is on the bench, that’s pretty normal.