Despite getting a lot of criticism for his performance in their defeat to Man City last weekend , Mourinho kept faith in Lukaku on Wednesday against Bournemouth and he rewarded him by scoring the winner.
The Belgian striker starts up front again at the Hawthorns, with Mata, Rashford and a revitalised Jesse Lingard supporting him. Anthony Martial is dropped to the bench.
Paul Pogba remains sidelined through suspension due to his straight red card in their win over Arsenal two weekends ago.
In his absence, Ander Herrera returns to the starting line-up in midfield having been rested against Bournemouth, partnering summer signing Nemanja Matic.
Henrikh Mkhitaryan remains conspicuous in his absence having started the season spectacularly but shunted to the sidelines by Mourinho when he fell out of form.
Antonio Valencia, Ashley Young, Chris Smalling and Phil Jones start in defence, with Marcos Rojo fit enough to make the bench after recovering from a head injury in the Manchester derby.
Pep Guardiola's Man City are currently 14 points clear of their city rivals having thumped Tottenham 4-1 on Saturday .
At the other end of the table, Alan Pardew has been parachuted into West Brom's hot seat and charged with steering them out of relegation trouble.
The new WBA manager makes one change to the side that held Liverpool to a stalemate on Wednesday, with summer signing Oliver Burke replacing Hal Robson-Kanu in attack.
Man Utd XI: De Gea; Valencia, Jones, Smalling, Young; Matic, Herrera; Mata, Lingard, Rashford; Lukaku. Subs: Romero, Lindelof, Rojo, Shaw, McTominay, Ibrahimovic, Martial.
West Brom XI: Foster, Nyom, Evans, Hegazi, Gibbs, Yacob, Livermore, Krychowiak, Burke, McClean, Rondon. Subs: Myhill, Robson-Kanu, Brunt, Barry, Rodriguez, McAuley, Field.