Derry have slipped down to fourth in the Airtricity League Premier Division after this draw at Richmond Park on Friday night.
Stephen McLaughlin fired in off a post to give City a 30th minute lead.
St Pat's hit back on the stroke of half-time with Danny North beating the offside trap before slotting past keeper Gerard Doherty.
Bray Wanderers leapfrog both Derry and Sligo Rovers into second place after a 3-0 win at Galway United.
Both sides created chances at a wet Richmond Park and Doherty made a series of fine saves to keep the Candystripes level.
Derry came close to snatching all three points when Danny Lafferty's free-kick on 74 minutes struck the woodwork.
Third-placed Sligo stay a point above Stephen Kenny's team after a scoreless draw at Bohemians.
Shamrock Rovers extended their lead at the top to three points after hammering UCD 6-1.
Dundalk were beaten 2-1 at home by Drogheda United in Friday night's other game.