Ronaldo made three goals in the first 25 minutes at Old Trafford, two for South Korea's Park Ji-sung and one for Wayne Rooney, who added his second before Bolton's Gary Speed converted a late penalty.

The victory moved the United to 75 points and a step closer to their first league title since 2003.

Chelsea are second on 69 points after a comfortable victory following early goals from Ukraine striker Andriy Shevchenko and Ivorian Salomon Kalou. Germany captain Michael Ballack came off the bench to head the third in the 58th minute.

West Ham United moved off the bottom with their first away win of the league season, a highly controversial 2-1 victory over Blackburn Rovers at Ewood Park.

Manchester City got a morale-boosting 2-0 win at Middlesbrough, while Tottenham Hotspur beat relegation candidates Watford 3-1, including a goal by Spurs' England keeper Paul Robinson with a free kick from his own half.

There were 0-0 draws between Reading and Portsmouth, along with Wigan Athletic and Fulham.