In scoring his two goals, 36-year-old Ronaldo became the first player in history to reach 800 goals in competitive games for club and country, doing so in 1,097 matches.
The game was watched by Ralf Rangnick, who replaces Michael Carrick as interim United boss after this game.
Carrick has since announced that he is leaving the club.
The result leaves United three points off fourth-placed Arsenal after recording two wins and a draw under Carrick.
Meanwhile Antonio Conte's unbeaten league start as Tottenham boss continued as they kept pace with the top four with a comfortable 2-0 win over a lacklustre Brentford.
A 12th-minute own goal from right wing-back Sergi Canos gave them the lead, before Son Heung-min finished off a scintillating counter-attack in the second half.
Tottenham climb to sixth - two points behind West Ham in fourth - while Brentford slip to 12th.