Dimitar Berbatov and Carlos Tevez both struck in the first period to make the game safe as Albion's run of three successive home wins came to a predictable end against the league leaders.
As an added bonus, United have now set a Premier League record of 11 successive clean sheets with goalkeeper Edwin van der Sar not having conceded a goal for 1031 minutes - beating the old record of 1025 minutes set by Chelsea's Petr Cech in 2005.
After a shaky opening 10 minutes, United, boosted by the return of Rio Ferdinand following an 11 game absence with a back injury, were never really tested.
Once Berbatov had scored his 11th goal of the season in the 22nd minute, the result was a formality.
Albion were facing even more of an uphill task five minutes before half-time when Paul Robinson was sent-off for the ninth time in his career for his challenge on Ji-Sung Park.
Tevez quickly added United's second with his 10th of the campaign before Nemanja Vidic and Ronaldo gave the scoreline an emphatic look.
Commendably for Albion they took the game to United in the opening stages and couldn't have imagined what they outcome would be after their bright start.
Marc-Antoine Fortune was picked out by Gianni Zuiverloon in the fourth minute and it needed a timely block from Vidic to frustrate the on-loan Nancy marksman.
But from the resulting corner by Chris Brunt, United had an even bigger escape when Michael Carrick had to clear Borja Valero's shot off the line.
Sixty seconds later, Albion's on-loan Arsenal striker Jay Simpson dispossessed Gary Neville only to see Ferdinand deflect his shot wide.
That let finally sparked United into life and Park gave a sign of what was to come when he picked up a pass from Carrick only to be denied by Albion goalkeeper Scott Carson.
Carson also did well to deny Berbatov but the England keeper was powerless to prevent the Bulgarian firing United into the lead.
Once again the impressive Carrick was to the fore, playing the ball into the path of Berbatov who clinically fired Carson.
United should really have doubled their advantage three minutes later when Ryan Giggs led a sweeping counter attack only for Carlos Tevez to stab Ronaldo's cross wide.
If Albion's task was not hard enough, it became even more impossible when referee Rob Styles had no hesitation in dismissing Robinson for his challenge on Park - one of a number of decision by the Hampshire official that infuriated the home fans.
United then quickly the game safe on the stroke of half-time when Giggs lifted a right-wing free-kick into the area.
Carson spilled the cross, claiming he was impeded by Vidic, and Tevez was on hand to stab the ball into an empty net from four yards.
It was then just a matter of how many rampant United would win by.
They had a brief scare when Ryan Donk hit the post, but any hopes Albion had of pulling off the greatest of comebacks ended when Vidic powered home a Giggs corner on the hour.
Just five minutes later, Giggs was again the provider, placing the ball into the path of Ronaldo who made no mistake from 14 yards.
Ronaldo made have been somewhat subdued by his own standards in the first half but he more than made up for it after the interval and helped himself to a second goal when he converted Berbatov's telling pass in the 73rd minute.