Eto'o hattrick dents United's hopes
This result left title-holders United 14 points adrift of leaders Arsenal with 16 league games of the season remaining and six off a place in the Champions League.
Their seventh league loss this term also turned the spotlight back on David Moyes, the successor chosen by Alex Ferguson, British football's most successful manager, to replace him following his retirement at the end of last season.
Eto'o gave Chelsea a 17th minute lead when his shot from just outside the box deflected off Michael Carrick.
The 32-year-old veteran Cameroon striker made it 2-0 on the stroke of half time when, following Gary Cahill's centre, he smashed the ball home from six yards out.
United, without injured strikers Wayne Rooney and Robin van Persie, were 3-0 behind four minutes after the interval when more lax defending from a set-piece allowed Cahill a free header.
His effort was blocked by United goalkeeper David de Gea but, barely a yard away, Eto'o reacted first and made no mistake as he become the first Chelsea player to score a hat-trick against United since Seamus O'Connell in 1954.
Javier Hernandez, on as a substitute for Ashley Young, pulled a goal back 12 minutes from time.
But that was as good as it got for United whose misery was compounded when captain Nemanja Vidic was sent off in stoppage time for a rash challenge on Eden Hazard, with Rafael de Silva then fortunate to escape a red card for an equally wild lunge on Cahill.
(File photo:Gallo Images)
- Sapa