Substitute Rafael volleyed United back into contention with a minute of normal time left - but Arsenal survived six extra minutes and an outbreak of mass anxiety attheEmirates to clinch the three points.
O'Shea scored from close range after Arsenal failed to clear a corner - giving United a slender but fully deserved advantage to take into the semi-final second leg attheEmirates next Tuesday.
In the UEFA Champions League round of 16 second legs Arsenal come close to pulling off a magnificent comeback but fall a goal short of pushing the game to extra time and beat Milan 3-0 attheEmirates.
War, terrorism and SARS may be sending large chunks of the airline industry into bankruptcy, but you wouldn't know it from looking at Dubai-based Emirates Airline.
Ramsey returned to theEmirates Stadium earlier in January, but Wenger now says the Caerphilly-born talent is back at his first club to build up his match fitness.