January signing Fernandes capped a man-of-the-match performance in style with his first goal for the club, nonchalantly converting a penalty he had won after being fouled by Ben Foster shortly before half-time.
Anthony Martial compounded the Hornets’ misery moments later with an exquisite chipped finish over Foster – his third goal in three games. Fernandes then set up Mason Greenwood for United’s third, the teenager’s explosive finish off the underside of the bar confirming an impressive victory over Watford.
Old Trafford paid an emotional tribute before kick-off to the late Harry Gregg, hero of the Munich Air Disaster, who passed away at the age of 87 last week. The first half would follow a frustrating script for United, whose attempts to bypass the Watford press resulted in them surrendering possession in dangerous positions time and time again.
Fernandes was hauled to the ground by the on-rushing Foster, leaving referee Martin Atkinson with no option but to the point to the spot, and the Portuguese hopped forward before stroking his first goal for the club into the bottom corner. And United rubbed salt into Watford wounds six minutes later.
Greenwood and Fernandes broke away on the counter and exchanged passes before the promising youngster fired an emphatic third in off the crossbar to wrap the victory, while Watford were sparred further damage when former striker Odion Ighalo struck the post late on.