In an open game with numerous opportunities at both ends, it was Bournemouth who triumphed because they were more lethal in front of goal.
Bournemouth were fortunate to be ahead at the break with a goal from Steve Fletcher, a close-range header from a centre by the ever-dangerous Wade Elliott.
Oldham should have been at least level but Neil Moss made a great save from Chris Hall who missed an easy chance just before the break with only the goalkeeper to beat.
Moss also turned over a header from Mark Bonner as Oldham went in at the interval regretting their missed chances.
Hall again with an open goal, allowed a pass from Kevin Betsy to run behind him.
Then Scott Vernon hung his head in shame after shooting over the bar with only the keeper to beat after John Eyre had played him clear.
Bournemouth made the most of their reprieves by going further ahead in the 60th minute and after that, the result was never in doubt.
Fletcher headed down a centre from John Spicer for O'Connor to score from ten yards.
Bournemouth went close several times as Oldham pressed forward desperately and James Hayter, Warren Cummings and sub Derek Holmes all went close.
Bournemouth's third was inevitable and it came in the 82nd minute when Hayter converted a low centre from Cummings for his 17th of the season.
Deep into stoppage time Bournemouth got their fourth when O'Connor drilled in a pass from another sub, Alan Connell
Oldham crashed to their 15th defeat of the season and their misery was compounded when they had central defender Daniel Hall booked for a foul on the elusive O'Connor in the 39th minute.