Nick Powell and Jesse Lingard scored for the Reds with Chuba Akpom netting twice for the North Londoners as the two teams put on an entertaining show on a tacky pitch.
A fast-paced opening failed to provide any real goalscoring openings, although Frederic Veseli fired in one dangerous centre and Reece Brown did well to block a Martin Angha cross at the other end. The first goal soon arrived, though, when United were guilty of conceding possession in the left-back area and Thomas Eisfeld's touch allowed Akpom to beat Michele Fornasier before ramming a near-post finish over Ben Amos.
The Reds' response was swift with Adnan Januzaj whipping in a left-wing free-kick after being fouled and Powell nipped in to nod home, even though Lukasz Fabianski got a hand to it. Isaac Hayden had to clear a Tom Thorpe header from a Januzaj corner as the hosts took a grip on proceedings.
On 22 minutes, a wonderful counter-attack strike edged United in front with Ryan Tunnicliffe releasing Powell, who showed great strength and patience to feed Januzaj and the Belgian's clever left-footed pass into the path of Lingard was finished stylishly by the winger.
After Thorpe was unable to convert a Januzaj free-kick, Tunnicliffe was desperately unlucky when his shot clipped the bar after good work by Lingard and Marnick Vermijl. Although the Reds looked in control, Arsenal hit back to level the scores on the half-hour mark. Conor Henderson's swerving shot deceived Amos and Akpom pounced on the rebound to net his second of the night.