The Saints defender praised his former boss ahead of the Premier Division clash between St Pat's and Dundalk at Richmond Park
The 28-year-old full back played under Dundalk boss Stephen Kenny for a period at Derry City in 2009 and has admitted that he is not surprised by the manner in which the Louth club has improved under his stewardship.
Last year, the Lilywhites narrowly avoided relegation to the First Division by defeating Waterford United in the relegation playoff, but this season they currently find themselves third in the Premier Division table, with eight points from five games.
"From having Stephen [Kenny] as a manager before, it's no surprise that Dundalk have improved on last year," O'Brien told the club's official website. "He has signed some good players and has looked to have really transformed the club."
He added: "They'll come to Inchicore looking to win, but if we can apply ourselves well, we can get a result."
Meanwhile, Saints boss Liam Buckley revealed that he is expecting a 'difficult game' from Dundalk and praised the 'quality group' of players that Stephen Kenny has assembled at Oriel Park.
"I saw the Louth derby last week and Dundalk showed great spirit to come back and draw 2-2, so we'll be expecting a difficult game on Tuesday," said Buckley.
"Stephen has put a quality group together that also have a huge amount of potential. They've made a great start to the league, and results home and away have been really impressive.
"At this early stage they've already got a decent haul of points, so we'll have to be on our game," added the Saints boss.
St Patrick's Athletic host Dundalk at Richmond in the Airtricity Premier Division this evening, Tuesday, April 2.