The visitors had the better openings early on with Matthew Spring curling an effort wide from 20 yards and Scott McGleish heading Dean Cox's free-kick over the bar from eight yards.
But Rochdale found their feet and created a host of opportunies with McGleish heading Craig Dawson's goalbound effort wide and Jamie Jones saving near-post efforts from Liam Dickinson and Nicky Adams.
The breakthrough arrived after 32 minutes when Brian Barry-Murphy's cross was glanced into his own net by Os defender Terrell Forbes.
Jones prevented Dale doubling their advantage before the break with good saves from Chris O'Grady and Alan Goodall and Dawson's header was hacked off the line by Charlie Daniels.
But Chorley levelled in the 60th minute when he met Paul-Jose Mpoku's corner with a firm header from eight yards, and Alex Revell almost grabbed a second with a volley just wide of the post.