With new interim manager Ralf Rangnick watching from the stands, the German turned into given a glimpse of each the skills he will ought to work with and issues he has to solve at Old Trafford.
Arsenal went in advance in bizarre situations as Emile Smith Rowe's shot trickled in with United goalkeeper David De Gea down injured before Bruno Fernandes levelled.
Ronaldo's 800th career goal changed into quick cancelled out via Martin Odegaard.
But the five-time Ballon d'Or winner had the final say when he crashed domestic a penalty 20 minutes from time.
A essential victory for United cuts the gap between the sides to two points in the conflict for an area in subsequent season's Champions League.
Three points also rounds off a first-class stint for Michael Carrick in caretaker charge considering that Ole Gunnar Solskjaer turned into sacked after progress to the Champions League remaining sixteen and a creditable 1-1 draw at Premier League leaders Chelsea.
The United fanatics paid homage to Solskjaer with a banner within the first fit at Old Trafford because he become disregarded.
However, once the motion got underway, nothing seemed to have modified from the very last days of the Norwegian's reign as United started out in a similar style to humiliating home defeats to Liverpool and Manchester City.
Pierre-Emerick Aubameyang and Ben White had possibilities for the visitors within the first two minutes.
