WONDER strikes from Morgan Amalfitano and super-sub Saido Berahino fired Albion into dreamland as they ended their near-35-year-wait for a win at Old Trafford in style.
The Baggies took the game to the champions in what proved to be a pulsating end-to-end encounter – and even coped with the early loss of Scott Sinclair to injury.
Following a goalless first half, summer loan signing Amalfitano produced an early goal-of-the-season contender nine minutes after the break to open the scoring.
The visitors’ lead lasted just three minutes as United skipper Wayne Rooney levelled from a free-kick.
But the new-look Baggies had more gas in the tank and fully deserved Berahino’s 67th-minute winner.
The 20-year-old's first Premier League goal put a smile on the face of club legend Tony ‘Bomber’ Brown – who scored twice the last time Albion won on United soil in 1978 - in the commentary box and the 1,500 fans who made the journey up from the West Midlands.
Clarke was forced to make two changes to the Albion side that beat Sunderland 3-0 last weekend, with Claudio Yacob and Victor Anichebe replacing injured duo James Morrison and Nicolas Anelka.
David Moyes made seven changes to the Red Devils team that lost 4-1 at Manchester City in the league in their previous top-flight outing.
The bonus for the Baggies that last season’s Premier League Golden Boot winner, Robin van Persie, was only fit enough to make the bench after a groin injury.
The visitors did well to weather early pressure from United but were dealt a blow in the 13th minute when Sinclair was forced off with a hamstring problem. Man-of-the-moment Berahino replaced him.
Moments later, Stephane Sessegnon produced a moment of magic to squeeze between Alexander Buttner and Shinji Kagawa out on the right to break to the by-line. The Benin international forced the ball into the six-yard box, where Michael Carrick twice did well to deny Anichebe.
The Red Devils swiftly countered in the 16th minute and Nani delivered a low diagonal ball into the box from the right that Javier Hernandez just failed to get on the end of, with Boaz Myhill forced to stretch out his right hand to stop it going in.
Albion then launched another attack and Yacob was caught late by Carrick, who ended up in referee Michael Oliver’s book.
Nani was in the thick of the action again on 20 as he flashed a ball across the six-yard box and just out of the reach of the lively Hernandez.
Four minutes later, United captain Wayne Rooney sent his ten-yard header straight into the arms of Myhill from Nani’s free-kick.
Another injury hit Albion in the 25th minute as Jonas Olsson walked off the pitch to have a cut above his right eye attended to after clashing heads with Hernandez.
The Sweden international was eager to get back on and returned to the battle with his head bandaged and his bloodied shirt changed.
Corner-taker Amalfitano produced a moment of brilliance just before the half-hour mark as he brought down a Liam Ridgewell pass on the left and whipped in a wicked cross. Berahino timed his run to perfection, only to send his six-yard header inches wide of the right-hand post when he should perhaps have given the Baggies the lead.
Rooney was also presented with a good chance on 33 but directed his ten-yard header from Nani’s centre well over.
The end-to-end play continued and on 37, Anichebe and Sessegnon linked up well to tee up Berahino, who curled a 20-yard effort just wide of the right-hand post.
Kagawa then tried his luck with a left-footed drive from just outside the box, but Myhill was able to comfortably gather low to his left.
Two minutes before the break, Kagawa laid the ball back in the penalty area for Buttner and he saw his goalbound shot well blocked by Olsson.
The Baggies then won a corner, which Amalfitano delivered for Yacob to flick towards the back post. Sessegnon was unmarked but blazed his volley high and wide from close range as he attempted to power it past the defenders on the goalline.
Anichebe crumpled to the floor seconds before the interval and limped down the tunnel on the half-time whistle, clutching his groin – but he re-emerged after the break.
In fact, it was United who made a change with Adnan Januzaj coming on for Kagawa on the left of midfield.
The visitors were packing a real goal threat and it was Sessegnon pulling the strings. Two minutes into the second half, the ex-Sunderland man teed up Berahino in the box but, with a free sight of goal, the youngster's shot was stopped by the feet of David De Gea.
But Clarke's side weren't to be denied, breaking the deadlock in the 54th minute - and how! Amalfitano surged forward with the ball from inside his own half and made the most of Sessegnon’s decoy run to nutmeg Rio Ferdinand before coolly dinking over De Gea.
The Baggies’ lead lasted just three minutes as Rooney’s in-swinging free-kick from the left evaded everyone and crept in at the back post. Myhill was helpless after being unsighted by Anichebe's unsuccussful attempt to block the set-piece.
Albion almost regained the lead seconds past the hour-mark as Olsson beat Ferdinand to Amalfitano’s corner and headed into the ground and off the crossbar.
The chances kept coming and in the 62nd minute, the impressive Anichebe again held the ball up well just inside the box before giving Sessegnon the chance to shoot just wide of the left-hand post.
The latter was proving dangerous again three minutes later and he was almost through on goal before Phil Jones brought him down 25 yards out and was booked.
From the resulting Amalfitano free-kick, De Gea pulled off a world-class save as the ball looked destined to find the top right-hand corner of the net.
But the Baggies got the goal their display had warranted by surging back in front on 67.
After terrific build-up play, Amalfitano laid off Sessegnon’s pass and Berahino crashed home a low left-footed finish from 20 yards – giving De Gea no chance.
Albion kept pushing for a third and Mulumbu did well to hold off Jonny Evans in the 80th minute and find Sessegnon, who sent his 15-yard volley wide of the right-hand post.
Moments later, Albion survived a scare as Nani got to the by-line and Olsson was forced to clear from inside the six-yard box, with Rooney lurking behind.
United thought they had found an equaliser five minutes from time when sub Marouane Fellaini converted Nani’s cross – but he was rightly adjudged off-side.
Myhill also had to be at his best in stoppage time to beat out Carrick’s pile-driver and Albion were then breathing a sigh of relief when Januzaj curled wide of the far post.
But a United equaliser would have been rough on the Baggies and Clarke's men held on to secure a famous win.
UNITED (4-4-2): De Gea; P Jones, Ferdinand, Evans, Buttner; Nani, Carrick, Anderson (Fellaini 67), Kagawa (Januzaj HT); Rooney (c), Hernandez (van Persie 58). Subs not used: Amos (gk), Evra, Welbeck, Valencia.
ALBION (4-2-3-1): Myhill; B Jones, McAuley, Olsson, Ridgewell; Yacob, Mulumbu; Amalfitano, Sessegnon (Rosenberg 90), Sinclair (Berahino 13); Anichebe (Lugano 88). Subs not used: L Daniels (gk), Dawson, Popov, Dorrans.
GOALS: UNITED – Rooney (57). ALBION – Amalfitano (54), Berahino (67).
BOOKINGS: UNITED – Carrick (foul 15), Jones (foul 67), Buttner (foul 73). ALBION – Mulumbu (foul 11), Amalfitano (foul 86).
REFEREE: M Oliver (Northumberland).
ALBION STARMAN: Morgan Amalfitano.