Petrol bombs were hurled over the barricade at Drumcree overnight, but the RUC described the trouble as "minor".
A crowd of about 400 gathered several hours after an Orange Order parade passed off peacefully, and several hundred stayed past midnight in front of the barricade blocking them from entering the nationalist Garvaghy Road.
Up to four petrol bombs were thrown, but they exploded harmlessly in the no-man's-land between the protesters and the security forces, an RUC spokesman said.
Protesters used a ladder to climb up and try and cut their way through the razor wire on top.
Despite the trouble, it was on a far smaller scale than in past years.
By 2 a.m. the RUC said only a handful of the crowd were left and described the situation as "quiet".
Security forces had staged a £6 million sterling operation to block nearly 1,500 Orangemen from marching on their traditional parade route along Garvaghy Road - a practice that has been blocked by objections from local nationalist residents for the past four years.
Members of the Portadown District LOL 1 staged a protest at the steel and concrete barrier blocking their path at Drumcree bridge but dispersed after pleas by their leadership for no violence.
PA