Sir Alex Ferguson believes Mexican striker Javier Hernandez has provided Manchester United with the extra firepower required to win the Champions League.

Hernandez helped United into the quarterfinals of Europe's elite club competition as his double strike secured a 2-1 win over Marseille in the last-16 second-leg match at Old Trafford on Tuesday.

The 22-year-old, nicknamed Chicharito, has surprised Ferguson with the speed of his development since arriving at United as a relative unknown from Guadalajara in preseason.

Ferguson expected the youngster to be an occasional understudy for Wayne Rooney and Dimitar Berbatov, but his impressive haul of 16 goals in all competitions has persuaded the United boss to leave Berbatov on the bench.

Ferguson was delighted with the way Hernandez combined with Rooney as United overcame yet another lethargic display to edge past the French champion.

Rooney set up Hernandez's fifth-minute opener and the Mexican displayed his predatory instinct again when he converted Antonio Valencia's cross in the 75th minute.

"Hernandez's pace and movement is helping us, he is a real handful. If you see the first goal he has made three runs before he scores," Ferguson said.

"The boy's movement is fantastic and I think Wayne is thriving on that, he is enjoying the freedom behind Hernandez.

"We are surprised how well Hernandez has done. When we brought him in we thought he would take some time adjust.

"He started as a sub and when he came on he won a few games. Now he has adjusted to the physical part and is lasting 90 minutes. That is giving us great options, with his form the way it is we can make some changes now."

It was fortunate for Ferguson that Hernandez was in such lethal form as United's overall display left much to be desired.

Marseille was a constant threat as a United defense already missing Nemanja Vidic and Rio Ferdinand was further hamstrung by injuries to John O'Shea and Rafael da Silva during the match.

Didier Deschamps' team wasted several good chances before Wes Brown's 83rd-minute own goal set up a tense finale and Ferguson conceded his side had struggled to cope at times.

"The balance of the team wasn't helped by two defenders coming off, especially when we were without Rio (Ferdinand) and (Nemanja) Vidic," he said. "That was our biggest problem. They are a very powerful, strong team and kept us under pressure with their deliveries into the box.

"There was a lack of experience and that could have cost us, but we hung on."

With so many defensive injuries, Ferguson was asked if he would consider bringing veteran rightback Gary Neville out of retirement just months after he hung up his boots, but the United boss said: "There's no chance! He hasn't trained for two months."

While the spluttering manner of United's performances raises questions about the team's quality, the Premier League leader is still on course for the treble.