The Reds got the better of Premier League rivals United 2-0 at home in the first leg of the Europa League last-16 tie.
Daniel Sturridge put Liverpool ahead in the 20th minute at Anfield, and Roberto Firmino added the second in the 73rd minute.
Henderson has thanked the Liverpool fans for their support against United.
"The fans were brilliant, electric,” the England international midfielder told BBC Sport (22:13). “That gave us a great boost.
“De Gea made some good saves, we created a lot of chances and we felt we could be two or three up.”
Looking back over the game! We deserved it, the mental strength and determination was just what @LFC needs!— Ian Rush MBE (@Ian_Rush9) March 10, 2016
Over the course of the 90 minutes at Anfield, hosts Liverpool had 56% of the possession, took 13 shots of which eight were on target, and earned seven corners.
Visitors United had 44% of the possession, took five shots of which only one was on target, and did not earn a single corner.
The second leg of the Europa League last-16 tie will be played at Old Trafford next week.
With Liverpool taking a 2-0 lead, the Merseyside outfit will have to be considered favourites to go through to the quarter-finals.