Pat Deans scored his first ever goal for Shamrock Rovers to give the Hoops their first win in three games and set up an intriguing top-of-the-table clash with leaders Shelbourne next week.
Rovers got back to winning ways away to St Pats and brought the Saints' surge up the table to a halt thanks to the 21-year-old, who was only on the pitch as a 13th minute substitute after Marc Kenny was forced to limp out of the action.
Dubliner Deans, who hasn't started a game for the Hoops since September, showed his class by rifling a 25-yard shot past Shay Kenny on 66 minutes.
Pats had enjoyed much of the possession and were made to pay the penalty for not taking advantage of a first-half opportunity to take the lead when they were awarded a penalty on 14 minutes after keeper Robbie Horgan took down Pats striker Liam Kelly in the box after Horgan miscontrolled a back-pass.
Former UCD man Robbie Griffin is normally deadly from the penalty spot but Horgan guessed correctly and dived to his right, pushing Griffin's effort out for a corner.
That was the Saints' best opportunity to take the lead because Rovers were a different side after the break, and the Hoops went close through Tony Cousins on 58 minutes before Deans made the breakthrough eight minutes later, while on 70 minutes Pascal Vaudequin shot wide after great work by Brian Byrne.