Quick-fire goals from Wayne Rooney and Juan Mata in the second half cancelled out Steven Gerrard's opener as United claimed early bragging rights over their Premier League rivals.
Substitute Jesse Lingard completed the scoring with a fine volley from the edge of the area in the 89th minute at Sun Life Stadium in Miami.
Liverpool were in control of proceedings after captain Gerrard converted a 14th-minute penalty but the Manchester club hit back in the second half.
Rooney - named captain for the fixture - put United on level terms in the 55th minute before Mata completed the turnaround with a goal of his own just two minutes later as Louis van Gaal's team ended their tour of the United States unbeaten.
Both teams will now return to England as they prepare for their Premier League openers, with United hosting Swansea City on August 16 and Liverpool entertaining Southampton the following day.
United were forced to make one change to the team that started against Real Madrid, with Javier Hernandez replacing the injured Danny Welbeck in attack for the club's final match in the United States.
There were five changes to the Liverpool starting XI, as Sebastian Coates, Kolo Toure, Jack Robinson, Lucas and Jordan Ibe all made way for Gerrard, Martin Skrtel, Mamadou Sakho, Glen Johnson and Philippe Coutinho.
United made a composed start in Miami and were unfortunate not to take a fifth-minute lead as Sakho was on hand to scramble the ball clear ahead of the onrushing Mata following Ashley Young's teasing cross into the six-yard box.
Substitute Luke Shaw was called upon in the eighth minute due to an injury to United wing-back Antonio Valencia.
Liverpool began to cause problems and Brendan Rodgers' men were awarded a penalty in the 14th minute after United defender Phil Jones fouled Raheem Sterling.
Gerrard stepped up and made no mistake from the spot, sending goalkeeper David de Gea the wrong way.
Liverpool controlled the half from that point with their high-tempo pressing causing United problems and the Merseyside outfit thought they had another spot-kick in the 33rd minute when Sterling was brought down under a challenge from Ander Herrera, but the referee waved away appeals.
Sterling was in the thick of action within five minutes of the restart, with his deflected shot flashing just wide of the post.
But whatever Van Gaal said during his half-time team talk worked as United restored parity 10 minutes into the second half courtesy of Rooney, who was on the end of Hernandez's cross to side-foot the ball into the far corner of the net - his fifth goal on tour.
It got better for United two minutes later when Mata beat goalkeeper Simon Mignolet from the edge of the area, albeit with a deflection off Sakho, before Lingard's fine finish late on.
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