The hosts had a half-hearted claim for a penalty early on as Gary McCabe fell theatrically in the area but his claims were rightly dismissed.
The carnival atmosphere prior to kick-off as Rovers raised the championship flag was quickly dispelled, as the visitors exposed their vulnerable opponents, especially on the right flank.
Two glorious headed chances were spurned in five minutes by Ross Gaynor and Mark Quigley respectively, with the crosses originating, once again, from the Hoops’ left-hand side before the game appeared to take a decisive twist in the champions’ favour midway through the half.
An over-hit through ball intended for Gary O’Neill was intercepted by Dundalk’s keeper Peter Cherrie, who hesitated fatally before his attempted clearance rebounded off O’Neill, and Cherrie’s red card for hauling down the Rovers front man 25 yards from goal was deserved.
Dundalk, who included new signings Colin Hawkins, Quigley, Byrne and Greg Bolger, in addition to loan acquisition Shane Guthrie, in their starting line-up continued to play the more cohesive football and deservedly took the lead in the 44th minute. Once again Byrne was centrally involved as he was clipped by Dan Murray inside the penalty area and the ex-Bohs man sent Mannus the wrong way for the game’s opener.
However, to the anguish of the visiting support, their lead lasted just two minutes. A cross from Billy Dennehy was scrambled clear by Guthrie into the path of McCabe whose shot from 22 yards had too much power for replacement keeper Paul Murphy.
Rovers seized the initiative four minutes after the restart when Hawkins and Murphy hesitated and Gary Twigg was on hand to head home into the empty net from eight yards.
Twigg doubled his side’s lead six minutes later, racing on to O’Neill’s through ball before making light of the tight angle with an emphatic lofted finish.
SHAMROCK ROVERS: Mannus; Sullivan, Stevens, Murray, Oman; McCabe, Turner (Rice, 77), Finn, Dennehy (Kavanagh, 71); Twigg, O’Neill (Kelly, 82).
DUNDALK: Cherrie; Madden, Osborne (Hector, 50), Hawkins, Guthrie; Kearns, Bennett, Bolger (Maher, 81), Gaynor; Byrne, Quigley (Murphy, 24).
Referee: Alan Kelly (Cork).