By Martyn Herman

LONDON, Nov 2 (Reuters) Portsmouth's unlikely challenge to the Premier League's established top order faces a severe examination on Saturday when they travel to Old Trafford to take on leaders Manchester United.

Champions Chelsea, behind United on goal difference, face Tottenham Hotspur on Sunday buoyed by their 2-2 midweek draw in Barcelona while third-placed Bolton Wanderers host Wigan Athletic on Saturday.

Portsmouth's remarkable escape from relegation under manager Harry Redknapp last season has blossomed into a challenge at the other end of the table, Saturday's 3-1 defeat of Reading leaving Pompey in fourth place.

The fact their superb start has been underpinned by players deemed surplus to requirements elsewhere speaks volumes for Redknapp's expertise in the transfer market.

In former Arsenal defender Sol Campbell, ex-Porto and Tottenham midfielder Pedro Mendes and another former Gunner, striker Nwankwo Kanu, Redknapp has built a formidable spine.

Kanu, whose career seemed in decline when Pompey rescued him from relegated West Bromwich Albion, has rewarded his new manager with seven goals.

''There was a lot of rubbish spoken about us being on the slide when we lost to Chelsea in the league and in a League Cup match against Newcastle recently,'' Redknapp told the club's Web site.

DECENT FOOTBALL ''We have played decent football in all our home matches and the aim is to keep up that standard.'' United look ready to battle Chelsea all the way for the title this season.

There is a mood of optimism sweeping Old Trafford, particularly with Cristiano Ronaldo, Louis Saha and back-in-form Wayne Rooney hungry for goals.

Rooney's hat-trick in the 4-0 thrashing of Bolton last week left manager Alex Ferguson purring.

Chelsea will be waiting to pounce on any United slip-ups when they travel to White Hart Lane, a ground where they have not suffered a league defeat since 1987.

Arsenal, in fifth place, travel across London to West Ham United on Sunday.

Seven points behind the joint leaders, albeit with a game in hand, Arsene Wenger's side can ill afford any more squandered points.

Teddy Sheringham, 40, who scored in last week's 2-1 win over Blackburn Rovers, is itching to take on Arsenal.

''It's the type of game you want to be involved in. The crowd will be up for it and we as players will be desperate to get another good result,'' said the veteran West Ham striker.

REUTERS PM HT855