Kevin Doyle's 10th senior international goal set the Republic Ireland on the road to a comfortable victory in Andorra as Giovanni Trapattoni's men completed the first half of their mission.
Doyle's seventh-minute strike gave Ireland an advantage they never threatened to surrender and when defender Ildefons Lima deflected Aiden McGeady's shot into his own net 13 minutes later, the points were effectively safe.
O'Shea went close to adding his name to the scoresheet when he headed just over the angle of bar and post from Duff's corner in the 74th minute.
In the meantime, Doyle had been replaced by Shane Long, and the West Brom striker was soon followed on to the pitch by Stephen Hunt as Duff made way.
The game was ebbing away tamely as the Republic dominated possession without creating anything of real note.
Long headed fractionally wide from Keane's 84th-minute cross, but Ireland had already done enough to ensure their fate remains in their own hands.
Russia's victory in Slovakia means they will win Group B if they beat the Andorrans at home on Tuesday evening, but a draw with Armenia will be enough to send the Republic into the Euro 2012 play-offs.