Javier Hernandez was Manchester United's Champions League hero as the Red Devils hauled themselves back from two goals down to beat Braga 3-2 at Old Trafford.

Approaching the 26th anniversary of Sir Alex Ferguson's appointment as Red Devils manager, the comeback was a suitably fitting way to preserve his side's 100 per cent record and means, barring a complete collapse in their final three games, they will advance to next spring's knockout stage.

A double from Alan, with United's defending looking suspect, put Braga 2-0 up within 20 minutes, but after Hernandez pulled one back soon after and Jonny Evans levelled after the break, the little Mexican capped a fine display by nodding home the winner from Tom Cleverley's cross 15 minutes from time.

However, with two games against Chelsea and a home encounter with Arsenal to come before the return fixture in a fortnight, Ferguson must harbour serious concerns about United's fragile defence. Incredibly, they have now fallen behind eight times in 12 games this season. It took less than two minutes to surrender the initiative.

Ferguson went for Michael Carrick as Jonny Evans' partner in defence, presumably on the basis Braga would not offer much of a physical threat. But Carrick lacks defensive nous and having shepherded Eder to the by-line, his failure to trap the Portugal international there was suicidal as, after turning sharply, Eder scampered towards the goal before cutting a cross back to provide Alan with an easy finish.

Alan then pulled back to the far post and climbed above Alex Buttner, replacing Patrice Evra for the first European game of his entire career, and steered past David de Gea to make it 2-0.

United were a threat themselves at the other end and a wise advantage by Serbian referee Milorad Mazic allowed Shinji Kagawa to profit from a foul on Robin Van Persie, crossing for Hernandez, who nodded home.

Ferguson hauled off Kagawa and introduced Nani at the break and the transformation was immediate as United sped down the flanks, pinning their opponents back. As the crosses fizzed across Braga's goal, the visitors' defending became increasingly desperate.

When Evans took a fresh air swipe at Van Persie's corner, the attempted clearance cannoned back off Elderson, allowing the Northern Ireland defender a second chance, which he duly prodded in. It was Evans' second goal in three games, not a bad return considering he had only scored once in his previous 131 appearances for the Red Devils.

From that moment it was only a matter of time before United got their winner. Cleverley provided it with a superb, deep cross from the right touchline and Hernandez, whose movement was akin to that he showed during his debut season, peeled away and headed home.