A 2-1 win cut Chelsea's advantage back to six points. The London club, who play Liverpool in the League Cup final on Sunday, retain a game in hand.

But by the time they play Norwich next Saturday, United could have reduced their lead to just three points if they beat Crystal Palace earlier in the day.

Ferguson acknowledged his side had been short of their best after a draining Champions League defeat by AC Milan in midweek. But he was unstinting in his praise for Rooney.

"He was by far our best player," the Scot said. "He was absolutely magnificent today. And he's a winner, he was one taking the baton up and making the run for the line. The whole day he was on song."

For most of the second half, after Gary O'Neill had cancelled out Rooney's sweetly taken opener, it looked as if Portsmouth, the last side to beat United in the league back in October, would defy the odds once more.

But Rooney had other ideas. With ten minutes left, the teenager collected a pass from Ruud van Nistelrooy in his stride and surged into the box before finishing with aplomb to make it six league wins in a row for Ferguson's side.

Ferguson revealed that Rio Ferdinand had missed the match with a hamstring injury while skipper Roy Keane was rested and Gary Neville came off injured at half-time.

While United continue to hold out hope that Chelsea will crack, Arsenal's lingering hopes of retaining their Premiership title appeared to have been crushed after a 1-1 draw at relegation-threatened Southampton that left them ten points behind Chelsea.

Everton are looking good to claim the fourth qualifying spot for next season's Champions League, with a 3-1 win at Aston Villa that left them eight points ahead of nearest rivals Liverpool.

Despite taking a point from Arsenal, Southampton were left further adrift of safety as a result of Crystal Palace's 2-0 defeat of Birmingham.

Two penalties from Birmingham old boy Andy Johnson lifted Palace four points clear of the drop zone, a margin that could prove just enough with only ten games left to play.

Southampton will nevertheless take heart from the way they responded against Arsenal after being reduced to ten men just before half-time, when David Prutton was sent off following ugly tackles on Mathieu Flamini and Robert Pires.

The champions Arsenal exploited their advantage almost immediately when Freddie Ljungberg put them ahead in first half stoppage time.

But the numbers were evened up six minutes after the interval, Robin van Persie receiving his marching orders after incurring a second yellow card with a bad challenge on Graeme Le Saux.

Peter Crouch headed in a well-deserved equaliser for Southampton in the 67th minute and Wenger made it clear he held van Persie responsible.

"When you are playing against ten men, the most important thing is to keep eleven players yourself," Wenger fumed.

"I told him at half-time that when the home team has a player sent off, the referee is under pressure to send off an opposing player who has already been booked."

Saints manager Harry Redknapp was no less forgiving of the "foolish and irresponsible" Prutton, who could be facing a lengthy ban after confronting and pushing the referee following his red card.

"He will get done, that's for sure, and the players are all sick about what he did," Redknapp said.

"Luckily they had a stupid player on their side as well and he obviously decided he was going to get himself sent off to make it a fairer game for us."

Wenger's mood was unlikely to be helped by the fact that Southampton's equaliser again exposed the defensive deficiencies that have dogged Arsenal this season.

Goalkeeper Jens Lehmann flapped hopelessly at a corner from his right and giant striker Crouch was left with a free header which he directed downwards and into the net off the underside of the bar.

Leon Osman scored twice for Everton while Australian Tim Cahill was also on the mark with Nolberto Solana replying for Villa, whose faint hopes of securing European football are receding fast.

In Saturday's other match, Spurs left it late but finally overcame London rivals Fulham at White Hart Lane with goals from Fredi Kanoute (78) and Robbie Keane (90).