There was nothing in the first half to hint of the excitement to follow. There were chances for Javier Hernandez from two excellent Luis Nani crosses, Anderson headed over a Shinji Kagawa cross, and Berahino glanced an Amalfitano cross a couple of yards wide. Then, just before half time, Sessegnon skied a Claudio Yacob flick-on.
The second half was marked by a drastic improvement from West Brom and a woeful drop-off from United, just as David Moyes inexplicably replaced Kagawa with Adnan Januzaj, who would go on to put in a dreadful performance reminiscent of Old Trafford antihero Bebe.
On the 54th minute, Amalfitano scored a superb solo goal, cutting in from the right, nutmegging Rio Ferdinand, and leaving David De Gea prostrate as the winger arrogantly chipped him.
United hit back almost instantly, when Wayne Rooney’s cross from the left hand side almost found Javier Hernandez’s diving header, but found its way past Myhill at the back post to equalise.
The scores were level for just ten minutes, as Berahino scored a wonderful goal. Sessegnon clipped a pass forward to Amalfitano, whose lay-off allowed Berahino to blast a left-footed shot from 20 yards past a static De Gea. West Brom thoroughly deserved their first Old Trafford victory in 35 years.
(Photo: Adnan Januzaj (left) endured a nightmare afternoon)
Pre-match: A much more attacking side for United in their first league game after defeat against Manchester City. Luis Nani and Shinji Kagawa start, and the underwhelming Ashley Young and Antonio Valencia are dropped.
30’: Chance! - Berahino is so close to opening the scoring, sending a glancing header wide after Amalfitano’s cross from the right.
34’ Anderson hits the bar! - Shinji Kagawa advances down the left having been set free by Michael Carrick. He turns onto his right foot, and crosses for Anderson to head against the woodwork.
54' - Goal! Manchester 0-1 West Brom! What a goal from Morgan Amalfitano. He picks the ball up on the wing. He casually drifts inside, Januzaj letting him go. Finally, Ferdinand jumps forward, Amalfitano nutmegs him, is clean through on goal. He jinks, putting De Gea on the floor, and chips smartly over the 'keeper.
57' GOAL! Manchester United 1-1 West Brom. Rooney equalises! Rooney whips in a ball across the six yard box. Hernandez aims to flick it on with a dive, but it evades him, and discombobulates Myhill, so much so the ball goes straight into the goal!
67' GOAL! Berahino scores! Manchester United 1-2 West Brom. Sessegnon clips a ball over the top for Amalfitano. Holding off Phil Jones' challenge, his one-touch lay-off finds Berahino, who blasts the ball past De Gea.
This was West Brom's first victory at Old Trafford in 35 years.
With 7 points, this is Manchester United's worst start since 2002-3. They went on to win the league that year, but it looks incredibly unlikely that they will repeat that.
West Brom have now won two Premier League games in a row having previously gone eight games without victory.
(Photo: A pensive David Moyes looks on)
TALKING POINT: David Moyes is out of his depth. Defeat against Manchester City and Liverpool was bad enough, but bringing on Adnan Januzaj for Shinji Kagawa means that fans can legitimately question any decision he makes in future.
MAN OF THE MATCH
Stephane Sessegnon (West Bromwich Albion): Able to keep possession anywhere on the pitch, and he rarely lost it when he made a pass. Without him they would not have scored the winger, and he troubled United throughout.
Manchester United: De Gea 6, Jones 5, Ferdinand 5, Evans 6, Buttner 5, Nani 6, Carrick 5, Anderson 6, Kagawa 6, Rooney 6, Hernandez 6. Subs: Januzaj 4, Van Persie 6, Fellaini 5.
West Brom: Myhill 6, Jones 6, McAuley 6, Olsson 7, Ridgewell 6, Yacob 6, Mulumbu 6, Amalfitano 7, Sessegnon 8, Sinclair 6, Anichebe 6. Subs: Lugano 6, Berahino 7, Rosenberg 6.
THE MATCH IN A TWEET
#MUFC 1-2 #WBAFC - Different team, same result. Chicharito, Nani and Kagawa all start but Moyes's misery goes on.
(Photo: Saido Berahino celebrates his goal)