FA Cup: Manchester United beat Arsenal 3-1 to reach the last 16. © AFP Alexis Sanchez came back to haunt Arsenal as the Chilean opened the scoring in Manchester United’s 3-1 FA Cup fourth-round win on Friday to maintain Ole Gunnar Solskjaer’s 100 percent record as caretaker manager. Manchester United’s winning run under the Norwegian is now eight games in all competitions and his decision to make five changes was vindicated as both Sanchez and the returning Romelu Lukaku had a huge impact. Lukaku set up both Sanchez’s opener and Jesse Lingard’s second for the visitors in a two-minute spell just after the half hour mark.Pierre-Emerick Aubameyang reduced Arsenal’s arrears just before half-time and the Gunners had plenty of chances to force a replay, but were denied by Sergio Romero as the rested David de Gea was not missed.Substitute Anthony Martial then sealed United’s place in the last 16 eight minutes from time.De Gea was the hero when United won 1-0 at Tottenham two weeks ago with a similar counter-attacking style, but Solksjaer believes his side have made progress even from that victory.”A massive step forward for us performance wise. The structure of the team was miles better compared to…