Here, Sports Mole analyses how the game was won on the South Coast.
On target: 8
On target: 3
Was the result fair?
Without a doubt. Southampton looked in control for the first 10 minutes and the last 10 minutes, but everything in between was Manchester United and a point, which looked on the table towards the end, would have immensely flattered the hosts.
In his pre-match notes, Ronald Koeman explicitly stated his intentions to exploit the defensive frailties of Daley Blind. True to his word, Southampton tested the midfielder - playing at centre-back - regularly early on, with Pelle resembling something of a schoolyard bully the way in which he dominated him. On the right wing, James Ward-Prowse proved himself a nuisance as he swung in a host of superb crosses and it seemed only a matter of time before the Saints scored from one - and they did.
The youngster whipped in a fantastic ball for Sadio Mane, whose first-time poke was superbly saved by David de Gea, but Pelle was on hand to roll home the rebound. It was fully deserved, yet it could, and should, have been two just minutes later when Pelle passed against the post following a slack ball from Chris Smalling. There was a sense that the miss may just come back to haunt Koeman's side and it did - eventually.
Suddenly, the hosts, who had won just once all season, were coming under far more pressure at the other end and, despite a suspicion of offside, Mata squared for Martial to equalise. Jose Fonte, who endured a torrid time in this fixture last season, was doing little to redeem himself, but centre-back partner Virgil van Dijk, on his home debut, bailed him out on a few occasions.
It was a loose back-pass from Fonte last season which Robin van Persie punished, and the Portuguese defender will know precisely how Yoshida feels after the right-back - who replaced Cedric Soares in the first XI - committed an identical error, with identical consequence after Martial slotted home a second.
At 3-1 down, Mane, who had switched with Ward-Prowse in the first half in a tactical tweak that undoubtedly affected Southampton, stood up a fine cross for Pelle to plant home a second on 85 minutes, but it was not enough for Koeman's side. They remain with just one victory from six now, and suggestions of second-season syndrome grow more plausible by the week.
Manchester United's performance
In truth, Manchester United never started. They drifted into the game at around the 20-minute mark, by which stage they were already a goal behind. Much of the pre-match spotlight was shining on United's left-back position after Luke Shaw was ruled out until May following a horror injury in the 2-1 Champions League defeat at PSV Eindhoven during the week. Marcos Rojo deputised and the Argentine defender looked unsteady, with Ward-Prowse enjoying plenty of time and space in which to pelt cross after cross into the danger zone.
In the middle of defence, Blind and Smalling also looked shaky early doors, and a terrible clearance from the latter almost saw Southampton double their lead when Pelle struck the post. They slowly and surely developed a foothold, though, and Memphis Depay - who was quiet throughout - sent a gilt-edged header over the bar. It was a sign of things to come, as the offside Mata squared for Martial, who did superbly to foil Van Dijk before tapping home the equaliser.
The 19-year-old showed the type of composure that at times eluded the man from whom he inherited United's number nine shirt: Radamel Falcao. With three goals, Martial is already just one away from equalling the Colombian's haul of four last season. There was an element of luck surrounding his second, but he raced on to Yoshida's back-pass and casually finished beyond Maarten Stekelenburg.
Louis van Gaal's side began to pass Southampton to death, and their third and killer goal had no less than 45 passes in the build-up. Depay did well to slam a low effort against the post as he finally sprung to life, but Mata rolled home the rebound. At the other end, De Gea showed why he is such a priceless asset with a number of world-class saves; the last of which came at the death to deny Victor Wanyama from snatching a point.
Van Gaal may be worried by their start, and the way in which they let Southampton back into the game, but there was a whole host of plus points in between and the positives certainly outweigh the negatives for the Red Devils this evening.
Sports Mole's man of the match
Anthony Martial: Not always involved, but the £36m teenager offered a further glimpse into his glittering future with a well-taken brace. First, he showed fantastic composure to deceive Van Dijk en route to equalising, before ruthlessly punishing Yoshida by stroking home a second after the break. His hefty transfer fee is being repaid on a weekly basis.
Pelle can stake a claim after his first-half miss, but it has to be Yoshida for the way in which he gifted Manchester United and Martial their second goal of the afternoon.
Mark Clattenburg only had to book Van Dijk and Fonte in what proved a quiet game for the Durham official. He had two Southampton penalty appeals to contend with but, to his credit, he got both decisions correct. Good game.
Southampton: It is Capital One Cup action for the Saints now as they travel away to MK Dons for a third-round clash on Wednesday.
Manchester United: Meanwhile, today's visitors return to Old Trafford now and prepare to host Ipswich Town in another League Cup clash on Wednesday. body check tags ::