Robin van Persie's superb header accounted for Barclays Premier League leaders Arsenal and catapulted Manchester United firmly into the title race on a tense afternoon at Old Trafford.
In a game of few chances, the Dutchman's first-half header from a Wayne Rooney corner made the tangible difference between champions and pace-setters, but the foundations for success were built on a magnificently dogged defensive display from David Moyes' men.
The United manager opted to field Phil Jones in a withdrawn central midfield role alongside Michael Carrick, safeguarding against the Gunners' advanced midfield threat, and the move almost totally stifled the visitors' creativity in central areas.
A forward four of van Persie, Rooney, Antonio Valencia and Shinji Kagawa, meanwhile, offered United plenty of attacking menace. A cagey opening to the game yielded plenty of possession for United, but the clear mutual respect shared by the sides meant a dearth of chances.
When United forged ahead, it was with virtually the game's first attempt of note. Moments after a dangerous Rooney cross had been headed behind, the England striker swung in an equally threatening corner which van Persie reached ahead of Olivier Giroud to help a fine header into Szczesny's top corner.
Though Arsenal responded positively, their first attempt on goal didn't arrive until Giroud's 36th-minute header, which sailed comfortably off-target. Steadier was the flow of bookings. Bacary Sagna and Mathieu Flamini were cautioned, the latter for a lunge on Phil Jones, himself booked moments earlier for an apparently legitimate aerial challenge on Szczesny.