Long regarded as the biggest game in English football, Sunday's encounter lived up to the billing with goals and excitement at both ends, yet it will be remembered for Gerrard's unceremonious exit.
The Anfield captain was left on the bench by boss Brendan Rodgers before being brought on at half-time, only to be dismissed by referee Martin Atkinson less than a minute after his introduction.
The visitors' task was made easier in the second half thanks to Gerrard's moment of madness, with Mata subsequently doubling United's advantage with a goal that on another day would likely have stolen the headlines.
He found the net with an acrobatic scissor kick, and Van Gaal's side were on their way to a five-point gap over Liverpool in the race for fourth place.
Daniel Sturridge netted a consolation with Liverpool's first shot on target with 21 minutes left, but the hosts never looked like mounting a comeback and had Simon Mignolet not saved an injury-time penalty from Wayne Rooney, United would have won even more convincingly.
The England man was teed up by international colleague Sturridge in the centre of the area but with the goal gaping, he could only turn his shot narrowly wide of David de Gea's post.
Gerrard was thrown into the fray in place of Lallana at the break, but he was soon making his way off the field in ignominy following a rush of blood.
He appeared to win the ball in the initial challenge with Herrera, but then stamped on the United man's leg, leaving Atkinson with little choice but to brandish a red card.
Liverpool's indignation was furthered when Mata left them with a mountain to climb, producing a stunning scissor-kick finish from Di Maria's lofted pass.
The hosts did rally, and they pulled one back in the 69th minute when De Gea allowed Sturridge's shot from Philippe Coutinho's pass to fly in at his near post.
Martin Skrtel then caught De Gea with a stamp that sparked unsavoury scenes at the end of a disappointing day for Liverpool, but another memorable renewal of one of England's most famous fixtures.
