After seeing his side emphatically scupper Sunderland with a four-goal salvo on Boxing Day, Sir Alex Ferguson had made a quartet of changes.
Patrice Evra, Ryan Giggs, Owen Hargreaves and the East End's favourite son, Carlos Tevez, returned to the fold in place of substitutes John O'Shea and Nani and the sick duo of Wayne Rooney and ex-Hammer Michael Carrick.
Indeed, the Argentinian ace, who almost single-handedly kept the Hammers in the Premier League last season, received a rapturous reception from all four corners of a sell-out Upton Park crowd, who soon saw Lucas Neill scorch an angled 25-yarder beyond Tomasz Kuszczak's far post inside the opening minute.
Curbishley had made just one change from the side that had drawn with Reading three days earlier, as Mark Noble came into a five-man midfield in place of Dean Ashton, who dropped to the bench.
And the England Under-21 midfielder should have opened the scoring on seven minutes after Hayden Mullins rocked the bar with a rising eight-yard shot but, somehow Noble fired the rebound over the top with the goal gaping.
United took full advantage of that let-off on the quarter-hour mark when the breaking Louis Saha sent Giggs galloping away down the left-flank and the Welshman duly invited the unmarked Ronaldo to head the visitors into the lead.
The busy Nolberto Solano had a penalty shout turned aside by referee Mike Dean and, as the interval neared, the Peruvian then tried his luck with a dipping 20-yarder shot that Kuszczak palmed out from underneath his crossbar.
Carlton Cole then nodded Noble's centre over the top to leave the Hammers unluckily trailing at the break and, early in the second half, Solano bent a 25-yard free-kick inches wide before retiring with a hamstring injury.
Midway through the second period the substituted Tevez left just as he had arrived, but the cheers for the South American turned to jeers as the presence of his replacement Anderson led Jonathan Spector to senselessly handle Saha's cross towards the Brazilian.
No-one has beaten Robert Green from the spot this season but, having already made a hat-trick of stops, the once-capped England keeper kept his gloves clean this time as Ronaldo inexplicably drilled the consequent penalty beyond the base of his right-hand post.
This time it was the Hammers who made United pay for their costly miss and they levelled on 77 minutes when substitute Ferdinand rose highest in the six-yard box to meet Noble's corner with a powerful header that ripped into the net.
An ecstatic East End was still coming to terms with that equaliser when Noble engineered the 82nd minute winner with a well-flighted free-kick that Upson nodded beyond the diving Kuszczak and under his right-hand angle.