Ole Gunnar Solskjaer began his time in charge of Manchester United with a comprehensive 5-1 win at Cardiff City.
Marcus Rashford gave United a great start, striking a swerving free-kick past Neil Etheridge after just three minutes.
United doubled their lead just before the half-hour, Ander Herrera's 25-metre shot deflecting in.
Victor Camarasa pulled a goal back for Cardiff through a 38th-minute penalty after Rashford had handballed.
But Anthony Martial restored United's two-goal lead four minutes before the break after a wonderful passing move.
Jesse Lingard made it 4-1 from the spot on 57 minutes after he had been fouled and got a second in the last minute.
After scoring five goals in a Premier League fixture for the first time since Sir Alex Ferguson's final match in charge in May 2013, Man Utd are sixth on 29 points.
The defeat drops Cardiff down to 17th on 14 points.
Cardiff City: 26 Dec v Crystal Palace (A)
Man Utd: 26 Dec v Huddersfield (H)