The French striker found the back of the net after having not scored since February 11 against Watford, making it 1-0 midway through the first half before Wayne Rooney doubled the lead shortly afterwards.
Martial joined Man Utd from Monaco in 2015 for an initial €50m which could eventually rise to close to €90m due to several add-ons included in the deal.
And one of those add-ons, a €10m payment after scoring 25 goals in all competitions for United, has now been triggered.
The 21-year-old forward arrived with little reputation in England, but he impressed by scoring 17 goals last season.
Martial has now scored eight goals in 34 games in 2016-17 - a considerably less impressive haul - after converting at Turf Moor in the 2-0 victory.
There are two other scenarios that could see the final fee United pay for the Frenchman rise to close to €90m, according to documents obtained by Football Leaks back in January 2016.
If Martial reaches 25 international caps with France – he is currently on 15 selections – they will pay another instalment of €10m, and another similar payment if he finishes in the top three of the Ballon d’Or voting at any stage during his stay.
United may also have to give Monaco a further sum should they sell him for over €60m, although this depends on which of the previous clauses are met.