Dutch master Bolo Zenden marked his last game for Sunderland with a goal to help the Black Cats to all three points at West Ham.
Zenden netted a sublime 17th-minute header to give his side the lead against the relegated Hammers before in-form Stephane Sessegnon added a second six minutes into the second half.
Substitute Cristian Riveros added gloss to the final score with a last-minute goal, his first for the club.
It was a comfortable victory for Steve Bruce's men, with a fifth league away win of the season ensuring they achieved the considerable feat of remaining unbeaten in London all season.
And the Black Cats profited from drama elsewhere as West Brom came from three goals behind to draw at Newcastle and ensure Sunderland would finish the season in 10th position - achieving manager Bruce's pre-season aim of a top-half finish.
Sunderland acquitted themselves well and will be grateful to keeper Simon Mignolet for an excellent display, plus the flicks and tricks of Sessegnon who was outstanding.
The Hammers were relegated by virtue of defeat at Wigan last week and never really looked at the races.
The returning Asamoah Gyan twice tested Robert Green from the edge of the box within the first five minutes, while Nedum Onuoha saw a golden chance go begging when he hooked the ball straight at the keeper in a scramble.
But United almost took a seventh-minute lead when Freddie Sears curled an angled shot towards goal from the right-hand apex of the box only for Mignolet to push the effort clear of danger.
Mignolet was then grateful to Onuoha for a superbly-timed clearance with Hammers closing in after he spilled Thomas Hitzlsperger's free kick, while Phil Bardsley pulled off an equally impressive block to deny James Tomkins from the resulting corner.
The visitors' defensive work was rewarded when Zenden, on his Sunderland farewell, came up with an excellent opener on 17 minutes.
Elmohamady found space to cross from the right and the Dutchman steamed in to loop a header over the stranded Green for his second goal in as many away games.
It could have been two just before the half-hour when Gyan's deft flick sent Sessegnon racing into space, but his shot from just outside the box was easily gathered by Green down low.
A cagey clash played in a predictably near-vacuum atmosphere - apart from the magnificent away supporters - meant opportunities were few and far between as the first half ticked away, though Mignolet did make a smart save in injury time to deny Zavon Hines after he nipped in front of Onuoha to meet Frederic Picquionne's cross.
Belgian Mignolet, surely one of the Premier League's most impressive bargain new boys this season, produced another excellent save to prevent the Hammers levelling just after the break, getting down at his near post after Jack Collison managed to sneak a low free kick around the wall and towards the bottom corner.
And again Sunderland followed up a West Ham chance with a goal thanks to a superb strike from Sessegnon.
The little man from Benin collected the ball from Zenden on half-way and, from the instant he took possession, there was only one thing on his mind.
Sessegnon left opponents trailing in his wake before lining up a shot from 25 yards and beating Green with a low drive right into the corner of the goal.
The £6m January signing from PSG has really caught fire of late, finishing the season with goals in each of his last two games and three in his last five.
By now Sunderland were cruising - Gyan cracked an angled shot wide and Jack Colback forced Green into a smart tip-over after profiting from some excellent approach play.
Zenden saw a drive deflected wide late on, while Mignolet capped a superb afternoon by racing out to bravely dive at the feet of sub Victor Obinna.
And it was left to sub Riveros to have the final say of 2010-11, crashing a shot beyond Green after taking a touch to control Jordan Henderson's cross in injury time.