Ashley Young looked lively on his return to the starting lineup and it was the England winger who picked out Welbeck inside the area in the fifth minute but the striker's shot was well saved by Adam Federici.
Reading struggled to create any chances in the first period and were frustrated by a United defence, which was marshalled well by Nemanja Vidic.
Federici was once again forced to come to Reading's rescue midway through the first half, keeping out Tom Cleverley's low drive before reacting quickly to deny Young from close range.
Nani came closest to scoring in the first 45 minutes after replacing the injured Phil Jones, with the Portuguese winger striking the post with a volley from outside the area.
Despite enjoying most of the possession, United's attempts to find a goal continued without reward until the half-time whistle was blown.