Sir Alex Ferguson declared on Friday the Premier League title battle was now a straight fight between his own side and the Gunners, and with trips to Chelsea and Liverpool looming, United could not have made a better start to their week on the road.
Preferred to Dimitar Berbatov, Hernandez justified the faith of his manager, turning home Nani's first-half cross before finishing Wayne Rooney's brilliant second-half through ball.
Rooney and Fabio then scored in the final minutes to leave relegation-threatened Wigan thoroughly deflated at a result that did not reflect their performance.
Three times Edwin van der Sar needed to make outstanding saves, whilst skipper Nemanja Vidic was a towering presence in the United defence.
Ferguson often speaks of his regret at failing to land Van der Sar in 1999 when he was searching for Peter Schmeichel's replacement.
At the time, the giant Dutchman was at Ajax and about to leave for Juventus.
Instead, Ferguson tried a number of alternatives. Some were better than others and titles kept being won.
But was not until Van der Sar arrived from Fulham in 2005 that concern about the goalkeeping position ended.
This summer, Ferguson must hope for more success as Van der Sar heads off into retirement, having hit the 40-mark but still capable of producing the brilliance that has categorised his career.
Two first-half saves were responsible for United having a half-time lead at the DW Stadium when they could easily have been behind.
A poor back-pass from Paul Scholes presented Victor Moses with the first opportunity.
Moses strode into the United box with only Van der Sar to beat. He failed, blasting his shot against his imposing opponent's chest.
That was when the contest was still goalless. Within seconds of United's opener, Wigan were in again.
This time Moses was the provider, drilling a low cross to the far post where the combative James McCarthy was on his own six yards out.
Again, only Van der Sar stood between Wigan and the net. Once more he came out on top.
That Hernandez had scored in between only added to the Latics' frustrations.
The Mexican, preferred to Dimitar Berbatov, tends not to look as dangerous when starting games.
He clearly knows how to find space, though. And, having once been denied by Ali Al Habsi after streaking clean through, the Mexican wriggled into enough space to steer home Nani's 17th-minute cross.
It was tough luck on Wigan, who were the better side, frustrating Scholes and Rooney in particular.
That Scholes avoided a booking for clattering into the back of McCarthy was a mystery to everyone but referee Mark Clattenburg.
Rooney had earlier caught the midfielder on the back of the head with his elbow.
The Wigan fans were incensed. Rooney pleaded his innocence. TV replays were inconclusive.
Before the half had ended, Rooney had needlessly got himself involved in a shoving match with Antolin Alcaraz and still looked ill at ease in the second period even though United played with far more poise.
They were forced to survive another near thing for Wigan before they took command, though.
This time, Van der Sar needed agility rather than reactions to deny Maynor Figueroa.
Nani came close to doubling the visitors' lead when he thrashed a fierce shot into the side-netting, not long after he had been repelled by Ali Al Habsi's firm one-handed save.
Ferguson made comparisons between Nani and Cristiano Ronaldo earlier this week.
United's current Portugal winger is certainly a major attacking threat and Al Habsi repelled him with the first part of a double save, when he also denied Darren Fletcher, who had been set up by Rooney.
The England man may still be struggling for goals himself but he remains an excellent source of them.
After failing to convert a close range header, Rooney collected Hernandez's knock-down, then fed the Mexican with a delicately weighted pass.
Clean though, the Mexican found the bottom corner with ease.
Victory assured, a Rooney tap-in from Berbatov's square ball, followed by Fabio's close-range finish, his first United goal, merely rubbed Wigan's noses in it at the start of an eight-day period when, one senses, the strength of their title credentials will be discovered once and for all.