Manchester United will have to maintain their best attacking form and overcome continuing injury problems when they bid to re-open a six-points lead over Chelsea by beating Middlesbrough on Saturday.

United went six points clear on Tuesday when they beat Sheffield United 2-0 at Old Trafford, but their lead was cut back to three points when Chelsea crushed West Ham United 4-1 at Upton Park on Wednesday.

The English Premier League leaders have been without up to six key defenders in recent weeks, but have made light of that setback with free-scoring performances as they seek a first title triumph since 2003.

A home victory over Middlesbrough would give them a six-points lead again -- for at least 21 hours -- before Chelsea continue their stubborn pursuit of United at Newcastle on Sunday afternoon.

With five matches to play United have 81 points and Chelsea have 78 -- with the two due to meet each other in the run-in on May 9. They will also meet in the FA Cup final at Wembley on May 19 and, possibly, in the Champions League final in Athens on May 23.

Despite missing such influential players as England defenders Gary Neville and Rio Ferdinand, Ireland's John O'Shea and Serbian Nemanja Vidic, United have lost only once in nine league games since a 2-1 defeat at Arsenal on January 21.

But they have conceded goals steadily and the absence also of French striker Louis Saha with hamstring problems has intensified the pressure on their star forwards to continue sparkling.

That loss was at Portsmouth and came during a spell when despite scoring 20 goals in seven games in all competitions, they also conceded seven and kept only two clean sheets -- one of those against Middlesbrough in a 1-0 FA Cup quarter-final replay victory a month ago.

NINE WINS

In the period since January20, Chelsea have reeled off nine straight wins and conceded only one goal -- at West Ham United on Wednesday when they won 4-1 -- since their last defeat at Liverpool on Jan 20.

The defending champions, hunting a third successive title under their Portuguese coach Jose Mourinho, have refused to buckle under the strain of attempting to win an unprecedented four trophies. They have won the English League Cup already.

And, now, with previously-injured players returning to fitness, they appear to be finding their best form again.

While the top two continue their duel for the championship, Liverpool and Arsenal seek to confirm their qualifying places for the Champions League next season.

Third-placed Liverpool are at home to struggling Wigan Athletic and Arsenal, fourth, face a difficult north London derby clash at local rivals Tottenham Hotspur, traditionally one of the more passionate occasions in the English season.

Tottenham, eighth, are pushing to climb a place in the table to reach one of the three UEFA Cup qualifying places currently occupied by Everton, Bolton Wanderers and Portsmouth. 

Coach Martin Jol will hope his inconsistent side can take advantage of uncertainty at Arsenal following a recent run of three league defeats and the shock departure of long-serving vice-chairman David Dein on Wednesday.

Bottom club Watford could be relegated if they lose at home to Manchester City while West Ham face Everton and Charlton Athletic meet fellow-strugglers Sheffield United.