United have 80 points with one match to play. Arsenal, the only other contenders, have 72 from 35 games and would concede the championship if they failed to beat Leeds United at Highbury on Sunday.
However, the race is far from over. If Arsenal win their two matches in hand, against Leeds and fellow Cup-finalists Southampton next Wednesday, they will move to within two points of United before the last games of the season on May 11.
Arsenal visit relegated Sunderland, which should give them another victory, but United have a tougher match at Everton.
But whatever the twists to come, it was all smiles for the leaders as Van Nistelrooy marked his 100th match for the club with a hat trick, taking his season’s tally to 43 - just three short of United’s record of 46 established by Denis Law in 1963-64.
Although it was the last home match of the season, the players did not perform the usual lap of the stadium.
Van Nistelrooy scored after 31, 38 and 53 minutes and has now bagged 79 goals for United.
The Dutchman has also found the target in his last 11 matches, including two internationals — and is the premier league’s joint top-scorer this season with 23 goals, the same as James Beattie of Southampton.
United took the lead after 11 minutes when Charlton defender Chris Powell failed to clear a high cross, allowing Beckham to chest the ball down before shooting. The ball took a deflection off Powell that gave goalkeeper Dean Kiely no chance.
But Charlton equalised less than two minutes later when United goalkeeper Roy Carroll, in for the dropped Fabien Barthez, sent a clearance straight to Claus Jensen, who scored with a first-time 30-metre shot with the keeper stranded.
Van Nistelrooy put United back in front with a hooked shot after Charlton failed to clear a corner, and made it 3-1 when he lifted the ball over Kiely.
The big striker completed his third league hat trick of the season after controlling a long, accurate cross-field pass from Beckham with one deft touch, sweeping the ball under Kiely in the next instant with an unstoppable low drive.
The victory made it 45 points from the last 51 available to United, who are chasing their eighth league title in 11 seasons.
Later Newcastle United clinched a place in next season’s Champions League qualifying competition when they beat Birmingham City while both Liverpool and Chelsea lost.
Hugo Viana scored Newcastle’s only goal in their 1-0 victory from a free kick after 42 minutes following a red card handed to City’s Matthew Upson by referee David Elleray, officiating in his last match before retiring.
Newcastle moved on to 68 points — four clear of both Liverpool and Chelsea who meet in their final game next weekend at Stamford Bridge.
Liverpool were beaten 2-1 at home by Manchester City with both goals being scored by ex-Liverpool striker Nicolas Anelka, the winner coming in injury time.
Chelsea stayed in fourth place despite losing 1-0 at relegation-battlers West Ham who won with a 71st minute goal from substitute Paolo Di Canio, back in the team for the first time since February.
Results:
Aston Villa 1 Sunderland 0
Blackburn Rovers 1 W.B. Albion 1
Fulham 2 Everton 0
Liverpool 1 Manchester City 2
Manchester United 4 Charlton Athletic 1
Middlesbrough 5 Tottenham Hotspur 1
Newcastle United 1 Birmingham City 0
West Ham United 1 Chelsea 0
Playing on Sunday: Arsenal v Leeds United—Reuters