Charlie Austin headed a winning goal on his Southampton debut at the weekend, helping the club to a second successive Premier League win at Old Trafford.
It was a miserable afternoon for Manchester United, who looked awful in the 1-0 defeat in front of their home fans.
The Red Devils offered little as an attacking force, and saw full-back Matteo Darmian taken off with an injury.
Austin's winner brought delighted for Liverpool forward Danny Ings, who sent him a message of congratulations via Twitter, clearly delighted with the way events unfolded.
The result was ideal for Liverpool, who had won a fantastic game earlier in the day away to Norwich City 5-4, thanks to an injury time winner from Adam Lallana.
Ings is currently out injured with a knee problem and expected to miss the rest of the season. Liverpool are only three points behind Manchester United, who are in fifth place in the Premier League table.