Alexis Sanchez made a goalscoring return to Arsenal to set Manchester United on their way to a fourth-round FA Cup win which makes it eight straight wins for interim manager Ole Gunnar Solskjaer.

Sanchez has struggled to produce his best form since swapping Emirates Stadium for Old Trafford a year ago but was at his sharpest to take Romelu Lukaku's superb reverse pass in his stride and round Petr Cech to give United a 31st-minute lead.

Lukaku was the creator again two minutes later as Jesse Lingard's precise finish doubled United's advantage - and even though Pierre-Emerick Aubameyang pulled one back before the interval, Solskjaer's side were always in control.

United keeper Sergio Romero's superb save from Aaron Ramsey at the start of the second half was crucial in keeping Arsenal at bay and United were rarely troubled afterwards.

Arsenal's cause was not helped by injuries to key defenders Sokratis Papastathopoulos and Laurent Koscielny; substitute Anthony Martial wrapping up United's latest success when he pounced after Petr Cech could only palm out Paul Pogba's shot with eight minutes of normal time left.