Their current position equals their lowest ever standing in the rankings, which they occupied for almost a year before embarking on their memorable Grand Slam-winning campaign in 2009.
New Zealand are another side licking their wounds after surrendering the Tri Nations title to Australia, Ireland's Pool C rivals, with a 25-20 loss at Suncorp Stadium on Saturday.
The defeat sees the All Blacks' cushion at the top of the rankings cut to only 1.71 points. They had sat 7.74 points above Australia when the Tri Nations began but after suffering back-to-back defeats for the first time since 2009, that cushion has been significantly eroded.
With the points exchange system used to calculate the IRB World Rankings doubling for all matches at the Rugby World Cup to reflect the importance of the tournament, Ireland could quickly climb back up the rankings list.
Australia's victory, which secured a first Tri Nations title for them since 2001, has stretched their advantage over South Africa in third to just over three points.
IRB WORLD RANKINGS (as of Monday, August 29):
Last week's positions in brackets -
2(2) AUSTRALIA 88.84
3(3) SOUTH AFRICA 85.69
4(4) FRANCE 83.78
5(5) ENGLAND 82.89
6(6) WALES 80.79
7(8) SCOTLAND 78.83
8(7) IRELAND 78.50
9(9) ARGENTINA 78.40
10(10) SAMOA 74.54
Ireland's other Pool C opponents:
11(11) ITALY 73.88
18(18) USA 65.00
19(19) RUSSIA 61.92