The Black Cats had no answer for first-half goals from Robert Snodgrass and Alex Tettey.
Gus Poyet's side remain three points from safety, however, as the teams above them failed to take advantage.
West Brom did not take anything from their trip to Hull, losing 2-0 to goals from Liam Rosenior and Shane Long.
Crystal Palace came close to making a point but were undone by a Papiss Cisse injury-time winner to lose 1-0 at Newcastle.
Swansea also lost 3-2 at Everton to remain just a point better off than the Eagles.
Wilfried Bony had cancelled out a Leyton Baines penalty but second-half goals from Romelu Lukaku and Ross Barkley secured a win that lifts Everton above Tottenham and into fifth.
Ashley Williams headed in an injury-time corner but it was too late for the Swans.
Premier League
West Ham 0 - 2 Man Utd
Cardiff 3 - 6 Liverpool
Everton 3 - 2 Swansea
Hull City 2 - 0 West Brom
Newcastle 1 - 0 C Palace
Man City 5 - 0 Fulham
Norwich 2 - 0 Sunderland
Chelsea 6 - 0 Arsenal
There was a bizarre case of mistaken identity as Arsenal embarrassingly capitulated in Arsene Wenger's 1,000th match in charge in a 6-0 loss to Barclays Premier League leaders Chelsea.
Wenger was last month called "a specialist in failure" by Jose Mourinho and remains without a victory in 11 attempts against his nemesis after a spectacular implosion and an horrendous mistake by referee Andre Marriner.
The Frenchman watched on helplessly after two goals in three first-half minutes from Samuel Eto'o and Andre Schurrle gave Chelsea a handsome lead inside the first 10 minutes before Marriner sent off Kieran Gibbs for a handball committed by Alex Oxlade-Chamberlain.
Eden Hazard's shot was handled in the area and, despite Oxlade-Chamberlain appearing to approach the official to admit wrongdoing, Gibbs was shown a red card in a decision which continues the debate over the use of television replays.
Hazard converted the penalty to give the Blues a 3-0 advantage after 17 minutes as once against the Gunners imploded at the home of a title rival following the heavy losses at Manchester City and Liverpool.
Oscar added a fourth before the interval, a fifth after 66 minutes and his replacement Mohamed Salah struck his first Chelsea goal as the Blues responded from the controversial loss at Aston Villa in emphatic fashion.
Arenal's defeat dropped them down to fourth in the table after Liverpool and Manchester City both also won by emphatic scorelines.
Liverpool twice had to come from behind before seeing off relegation threatened Cardiff 6-3.
Luis Suarez finished with a hat-trick but the forward and Martin Skrtel first had to cancel out first-half strikes from Jordon Mutch and Fraizer Campbell to make it 2-2 at half-time.
Skrtel then fired the Reds ahead on 54 minutes before Suarez lashed in Daniel Sturridge's clever flick on the hour. Suarez returned the favour soon after for Sturridge to tap in.
Mutch pulled one back, but Suarez had the final say in injury-time.
City chalked up a simple 5-0 win over bottom-of-the-table Fulham on the back of a Yaya Toure hat-trick.
The Ivory Coast midfielder scored a penalty in each half, the second after Fernando Amorebieta saw red, before bending in a long-range strike on 65 minutes.
Fernandinho and Martin Demichelis struck late on to ensure City joined their title rivals in racking up a big score.
Wayne Rooney produced his own David Beckham moment to put Manchester United on course for an impressive 2-0 victory at West Ham, firing home one of the most memorable goals of the season from 58 yards.
Returning to league action after progressing to the Champions League quarter-finals with victory against Olympiacos, the England international netted twice as David Moyes' men proved Wednesday's result was no flash in the pan.
Rooney's second saw him move onto 212 goals and usurp Jack Rowley as the third highest goalscorer in United's history, but it was his first just eight minutes into the 2-0 victory that will live long in the memory.
The 28-year-old produced a moment of magic, sending the ball sailing over Adrian in a goal similar in audacity and skill to Beckham's wonder strike at Wimbledon in 1996.
Rather aptly, the former United midfielder was at Upton Park to witness the effort first-hand and will have been impressed by the way Moyes' side held on to condemn West Ham to a third successive defeat.