Icelandic striker Heidar Helguson scored his ninth goal of the season to put Neil Warnock`s men ahead in the 37th minute but North End gradually improved after the restart.
And midfielder Nicholson struck a superb effort from 18 yards in the 64th minute to level matters at 1-1 for the hosts.
However, Preston remain without a win since Phil Brown took the helm at the start of last month.
QPR, meanwhile, still hold a five-point lead at the summit after Cardiff lost 2-1 at fellow promotion rivals Nottingham Forest, who themselves moved up into second place.
Source: PA
Source: PA