The last time a United player scored a hattrick against Liverpool was September 11th 1946 at Maine Road. Stan Pearson was the fella to do it. Jack Rowley opened the scoring, Pearson then grabbed his hattrick, before Charlie Mitten made it 5-0, on just his 4th appearance for the club.
The last time a United player scored a hattrick against Liverpool at Old Trafford it was Joe Spence on May 5th 1928. He scored the opening three goals before Jimmy Hanson made it four and Bill Rawlings added another two to make it 6-1.
Dimitar Berbatov, welcome to your spot in Manchester United history.