Icelandic striker Heidar Helguson scored his ninth goal of the season to put Neil Warnock's men ahead in the 37th minute on Saturday but North End gradually improved after the restart.
And midfielder Nicholson struck a superb effort from 18 yards in the 64th minute to level for the hosts, who remain without a win since Phil Brown took the helm at the start of last month.
Preston went close inside the third minute when a cross by David Gray was greeted by Nathan Ellington, whose right-footed shot from 12 yards out drew a fine block from Rangers defender Clint Hill.
Moments later the visitors fashioned their first opening when playmaker Adel Taarabt hit a fierce shot from 18 yards which forced a fine stop from Preston's on-loan goalkeeper Iain Turner.
In the 14th minute, the hosts went close again when an inswinging corner from the impressive Keith Treacy was met by a firm header from defender Sean St Ledger which flew wide.
Yet again the pendulum swung back in Rangers' favour and, after Leon Cort fouled Helguson, Taarabt hit a free-kick from 30 yards which drew another fine save by Turner, who tipped the ball round a post.
QPR's Alejandro Faurlin then drilled an 18-yard free-kick over the crossbar before Treacy had an effort blocked by Rangers' Matthew Connolly.
Rangers midfielder Wayne Routledge and North End striker Nathan Ellington both went close before the visitors forged ahead with their first meaningful goalscoring opportunity in the 37th minute.
Ishmael Miller showed his quality on the left flank with a fine cross that Helguson met with a right-foot finish high into the net from six yards out.
Preston almost responded immediately but Johnson had a shot saved by Paddy Kenny in the Rangers goal.
Two minutes after the restart, Rangers almost doubled their lead but Helguson headed against the crossbar.
Preston boss Brown then replaced Johnson with Paul Hayes in the 55th minute and the move breathed new life into the hosts as an attacking force.
They were level in the 64th minute when Ellington's neat header gave Nicholson the space to his a superb right-footed shot into the top corner from 18 yards.
Ellington then drilled an effort over the crossbar before Taarabt hit an effort just wide of the mark and then drew a smart stop from Turner.
Warnock made a change in the final quarter as Rob Hulse replaced Helguson up front.
Preston had chances in the closing stages as they sought to find a winner but Rangers held firm to hang on for a hard-earned point.