Anthony Martial continued his dream start to his Manchester United career by hitting two goals to lead his side from behind to a 3-2 victory over Southampton at St Mary’s. The visitors had looked in trouble when Graziano Pellè gave Southampton a richly deserved early advantage. But, with the same coolness he displayed when marking his debut with a fine goal against Liverpool last weekend, Martial pulled his new team level before the break.

And things were to get better still for the player United made the world’s most expensive teenager earlier this month. Gifted an errant back pass from Maya Yoshida, Martial nervelessly slotted the ball home. Juan Mata then notched a third with just over 20 minutes remaining, and despite Pelle’s late header, United held on to move up to second place in the table and, rather improbably, just two points behind leaders Manchester City.

Yet for much of the encounter it again looked some way short of being a vintage Manchester United performance. In the early going, they, and Michael Carrick and Daley Blind in particular, were overwhelmed by the pace and intensity of Southampton, as embodied by Sadio Mané . There was plenty of evidence why United had tried to sign the Senegalese attacker in the summer, and it was his shot that led to Pellè striking the game’s opening goal on the rebound. Indeed Mané could easily have helped propel Southampton to a more emphatic lead in the first 30 minutes. After Mané pressed United into a mistake, Pellè hit the post when the goal was calling.

Instead it was the player United did end up signing who continued to suggest that his eyebrow-raising £ 36 million fee may eventually prove justified. Still, United were given a helping hand from the officials, with Mata clearly offside before he squared for Martial to turn Virgil van Dijk and beat Maarten Stekelenburg in the 34th minute.

In handing a first Premier League start to the 19-year-old France international, Louis van Gaal had withdrawn Wayne Rooney into a deeper role. But, despite having plenty of possession, the far greater attacking threat to that point had come from Southampton. Martial’s goal, though, proved the catalyst for an improved Manchester United display and a welcome win after a defeat at PSV Eindhoven in midweek.

They still got plenty of help along the way, however. Yoshida’s pass back five minutes after halftime was suicidal to allow Martial to net his second, and the Southampton defending wasn’t much better when Memphis was given time in the box to strike a post before Mata had time to stroke home the rebound.

But this was a victory that showed the benefits of Manchester United’s, at the time much criticized, business in the closing hours of the transfer window. While it is far too early to get carried away about Martial’s ability, what he has given United is a much livelier threat in the final third than Rooney had provided. And at the other end, the team reaped the rewards from continuing to have one of the world’s very best goalkeepers between the posts. With United’s lead still at 2-1, David de Gea pulled off a sensational one-handed save when Jose Fonte’s near-post header had already gone beyond him and looked certain to ruffle the net. While the Spaniard’s long-term future remains uncertain, his ability to single-handedly earn United points cannot be overstated.

That is especially true given how vulnerable the defense in front of him remains at times. After Pellè was allowed to head in Mané’s cross, De Gea was required to intervene on more than one occasion to ensure his side walked away from the south coast with maximum points.