Giggs turned 36 on Sunday but boss Sir Alex Ferguson believes the Welshman has at least two years left in his legs, with his performance against Avram Grant's men illustrating his importance to United.

Pompey were on top at the break when the scores were level but Giggs set up Wayne Rooney to grab the lead back, he earned a penalty for his team-mate to net his hat-trick then added the fourth goal himself to join the league's centurions.

"It is about time I got 100 Premier League goals," he said.

"I am obviously proud of the achievement. There are not many players who have done it. Hopefully there will be many more."

Giggs' maturity appears to be rubbing off on Rooney, who has recently become a father for the first time and on the pitch has captained England.

"Giggs is amazing," Rooney said. "He never surprises you. His energy and work rate, passing, and movement is unbelievable. He is a privilege to play with.

"You wouldn't think he was 36, he plays more like a 26-year-old. He is up and down and everywhere. It is great for him he got 100 league goals."

The 4-1 defeat for Grant in his first match in charge of Pompey offered plenty of reminders of his final game for Chelsea 18 months ago, starting with the downpour.

It was teeming down in Moscow too for that Champions League final which was decided by penalties, while this match contained three spot-kicks. In Russia, Giggs effectively scored the decisive penalty and here he wrapped up the scoring with his free-kick.

The Pompey team Grant inherited had decent spells and the scoreline appeared to flatter United.

Rooney admitted: "The manager was quite disappointed we hadn't moved the ball around in the first half the way we can. We didn't create much and we had to work on that."

Pompey's performance brought the best out of goalkeeper Tomasz Kuszczak, who was preferred to Ben Foster in the absence of Edwin van der Sar, who picked up a knock to his knee against Everton the previous weekend.

"In fairness to Portsmouth they had some good chances," Ferguson said.

"Tomasz made three fantastic saves, there was no doubt there because his performance was top level and I was pleased with that."

Grant felt his side deserved more from the game and could have built on Kevin-Prince Boateng's penalty.

"If I came from the moon and saw the scoreline I'd think Manchester United played great and Portsmouth were not so good but we played very well," Grant said. "We played better.

"Our target is to stay in the league. It's not so easy because we are at the bottom, in last place, but it is possible. It will not be easy but it's possible because we played good football and the spirit was good. There are things we need to do better."

Grant is relishing his return to the dug-out, adding: "I enjoy to be involved in football - as a director or on the touchline. I like the pressure of football and the responsibility but I don't like it that we lost.

"We need to take points. We play against teams close to us, in our league, and we can win them."

Grant also expects to add players to his squad in January.

"The squad is good but we want to make is stronger," he said.

"We have positions where the team can be made stronger and we will do it. There is also the African Nations Cup and we will miss a lot of players."