Wayne Rooney singlehandedly dragged Manchester United back into the Barclays Premiership title race just as Portsmouth threatened to push Chelsea even closer to the finishing line.

Had it not been for Rooney's late winner at Old Trafford, United would have been trailing Jose Mourinho's men by eight points with time fast running out in their bold bid to catch the league leaders.

As it is, the gap could be down to just three points if United win at Crystal Palace next Saturday before Chelsea visit Norwich in the evening kick-off.

And it was all thanks to Rooney, who had seen his seventh-minute opener cancelled out by a superb volley from Portsmouth's Gary O'Neil 90 seconds after the restart.

He refused to let the visitors interrupt United's dogged chase of the leaders and, nine minutes from the end, delivered a blow which will have caused Portsmouth and Chelsea equal pain.

After cutting inside Dejan Stefanovic with a magnificent first touch as he strode onto Ruud van Nistelrooy's through-ball, Rooney refused to panic as he charged into the area.

Instead, it was Pompey keeper Kostas Chalkias who blinked first, losing his balance as Rooney raced towards him. By the time the striker was ready to shoot, Chalkias was on his backside and Rooney simply rolled the ball past him.

On the United bench, Sir Alex Ferguson must have breathed a huge sigh of relief.

After Wednesday's loss to AC Milan, a defeat which cost beleaguered keeper Roy Carroll his place, anything other than victory would have been a disaster for United.

Arsenal had already provided some concrete evidence for Mourinho's bullish attitude to his team's position by failing to dispatch Southampton at St Mary's, so United headed into battle knowing they were the only team left who can topple Chelsea from their lofty perch.

A fast start was not strictly essential, and might not have been expected given Ferguson's five changes, but after the midweek heartbreak to Milan, when it came it should have provided a galvanising effect on the home troops.

Van Nistelrooy wasted little time in making his presence felt on his first league start since the win at West Brom on November 27 and the prolific Dutchman was heavily involved in Rooney's opener even though he did not actually touch the ball.

So desperate was Pompey skipper Arjen de Zeeuw to snuff out van Nistelrooy's threat when Gary Neville swung over his right-wing cross that he leapt straight over the striker, flattening him completely, a move which totally backfired as the ball drifted over both of them and landed straight at Rooney's feet.

With the swiftness of someone in red-hot form, the £27million former Everton man swept home a first-time shot to launch what should have been a one-sided canter to victory.

But it did not materialise, partly because United inexplicably took their foot off the pedal and also because Portsmouth bravely refused to subside.

They should still have been two goals adrift by the break though as Rooney delivered a superb far-post cross to Neville, who teed up Cristiano Ronaldo with a perfect lay-off.

For all his many talents, Ronaldo has not yet - unlike Rooney - discovered the art of a clinical finish and could only balloon his volley high into the Stretford End.

It was a miss which would come back to haunt Ferguson's men within 90 seconds of the restart.

By that time United had lost Neville to an ankle injury sustained in a heavy but legal challenge with Matthew Taylor.

Ferguson's side were still readjusting to the switch which saw Alan Smith introduced and Phil Neville slot into the vacant full-back berth when O'Neil struck.

After complaining at the way his defence stood off Clarence Seedorf in the build-up to Milan's winner on Wednesday, Ferguson must have been aghast to see Steve Stone afforded the same treatment as he advanced towards the United box.

Stone was eventually stopped but as the ball bobbled around, Wes Brown could only knee it into O'Neil's path.

The England Under-21 skipper will probably never hit a volley as well again, the curl off the outside of his right boot taking it well out of Tim Howard's reach as the American desperately tried to keep it out.

It should have been the catalyst for United to shrug off their lethargy and rip Portsmouth apart.

Instead it brought only frustration, which increased by the minute as their title hopes began to drip agonisingly away.

It appears however that United's youngest player possesses in abundance the never-say-die spirit which has typified his manager's 18 years at the Old Trafford helm.

Mourinho might still have the air of a man who can feel destiny approaching but in his Cardiff hotel, with his side's lead cut to six points, he probably shifted uncomfortably in his seat as United's ecstatic players submerged their newest hero.

Teams:

Man Utd Howard, Gary Neville (Smith 45), Brown, Silvestre, Heinze, Ronaldo, O'Shea, Scholes (Giggs 65), Phil Neville, Rooney, van Nistelrooy (Fortune 85).

Subs Not Used: Saha, Ricardo.

Booked: Phil Neville.

Goals: Rooney 8, 81.

Portsmouth Chalkias, Griffin, Stefanovic, De Zeeuw, Taylor, Stone, Skopelitis, O'Neil (Kamara 84), Hughes (Mezague 54), Yakubu, LuaLua.

Subs Not Used: Hislop, Primus, Fuller.

Booked: Taylor, Griffin.

Goals: O'Neil 47.

Att: 67,989

Ref: M Halsey (Lancashire).