And in a game that Sir Alex Ferguson justifiably protested his side simply did not deserve to lose, it was skipper Nigel Reo-Coker who fittingly ended a week of harsh criticism to seize all the three points for West Ham with a 75th-minute winner.
Following mid-November's Icelandic takeover, it had been all change in the East End on Monday, when Alan Pardew paid the price for a shambolic start to the season that had seen West Ham win just four of their opening 20 league and cup matches.
Inheriting a side that had surrendered so meekly to Everton, Wigan Athletic and Bolton Wanderers in its last three games, newly-installed Hammers boss, Curbishley - who had never beaten United as a manager - quickly made three changes from the team that had lost 4-0 at the Reebok Stadium, last Saturday. Anton Ferdinand, Lee Bowyer and Bobby Zamora came in for Christian Dailly and substitutes George McCartney and Carlos Tevez.
Ironically, Curbishley's last game in charge of former club Charlton Athletic had been against United and, indeed, he had sought the wise counsel of Ferguson before deciding to end a seven-month sabbatical and step into that Hammers' hot-seat.
Ferguson's unchanged team needed no greater pre-match motivation than to sit in the Upton Park dressing room watching Chelsea's 3-2 win at Goodison Park, which reduce the Red Devils' lead to just two points, 20 minutes before kick-off.
Certainly, with five away wins on the spin, the Premiership pace-setters flew out of the traps as Wayne Rooney fired inches over, before Rio Ferdinand's header back across goal only needed a touch and Loius Saha forced man-of-the-match Robert Green to palm his low 18-yarder aside.
But with the East enders equally looking to impress the new boss, the diving Matthew Etherington carelessly headed wide with just the exposed Edwin Van der Sar to beat, while Marlon Harewood spun and sent a dipping 20-yarder whistling inches over.
And on the half-hour mark, Zamora out-muscled Ferdinand as they raced on to a lofted throughball, but as the red-faced former Hammers' defender tumbled to the Upton Park turf, he had Van der Sar to thank for somehow blocking the striker's point-blank effort.
Back at the other end, the lively Cristiano Ronaldo gave the Hammers a few anxious moments, before the stooping Rooney sent a header across the face of goal and, only the agility of Green, kept it goalless when Saha tested him with a couple of late first-half efforts.
Just after the restart, Ronaldo's tricky 35-yard free-kick free-kick bounced awkwardly in front of Green and then Ryan Giggs cut in from the right and tested the Hammers' keeper with another low 20-yard shot.
On 55 minutes, the breaking Ronaldo looked set to break the deadlock, but Green incredibly extended his left arm to divert the ball around his left-hand post to leave the Portuguese playmaker looking to the skies.
Moments later, Giggs was looking to the heavens, too, having wastefully launched the ball into orbit from all of eight yards.
The heroics of Green, allied to the Red Devils' wastefulness, was to pay dividends for workaholic West Ham.
And with just a quarter-of-an-hour left, substitute Teddy Sheringham stroked a sublime pass to the feet of Harewood at the near-post and his turn and cross into the six-yard box was met by the inrushing Reo-Coker, who gleefully stroked home the winner that sent out tremors at both ends of the Premiership table.