Cristiano Ronaldo marked his return to Manchester United and the Premier League with a stoppage-time goal to give the Red Devils a 1-0 lead at half-time over Newcastle.
The 36-year-old could not really miss from close range after goalkeeper Freddie Woodman fumbled a Mason Greenwood shot, leaving Ronaldo a simple tap-in.
The 36-year-old completed his move from Juventus on deadline day and was thrust straight into the starting line-up on Saturday.
Fellow marquee summer signings Raphael Varane and Jadon Sancho also started as Ole Gunnar Solskjaer made two changes, with Nemanja Matic coming into the side that beat Wolves along with Ronaldo.
Newcastle made four alterations to their 2-2 draw against Southampton, including Joelinton replacing the injured Callum Wilson.