A bigger winning margin could have lifted Ireland to third, equalling their highest position since the IRB World Rankings were introduced in October 2003, but the defeat was enough to see Australia surrender second spot to South Africa.
Defending champions South Africa's 49-3 win over Fiji in Pool D did not have any impact on either side's rating points, but the islanders do climb one place to 14th as a result of Tonga's defeat to Canada earlier in the week.
Tonga are the week's biggest fallers, dropping three places to 15th after the 25-20 loss to Canada in Whangarei last Wednesday and now lie only three-tenths above Georgia, the margin the European Nations Cup champions lost as a result of their 15-6 defeat to Scotland the same day.
Canada's success had provisionally lifted them to 12th, but Samoa's 17-10 loss to Wales resulted in another place gain to record their highest-ever ranking.
The Canucks' subsequent 46-19 loss to France in their Pool A encounter in Napier on Sunday did not affect the rating of either side.
Samoa's first ever loss to Wales in a Rugby World Cup saw them slip two places to 12th with Italy the other beneficiary despite not playing a match in the last seven days.
The other nation on the rise are USA following their 13-6 victory over Russia in New Plymouth. The Eagles' first World Cup win since 2003 lifts them one place to 17th, taking them above Romania.
Romania lost 43-8 to ninth-ranked Argentina on Saturday, but this had no impact on the rating points of either side. Russia were not as fortunate, their World Cup debut defeat by USA resulting in a two-place fall to 21st with Namibia and Portugal the beneficiaries.
The participating nations at the 2011 World Cup now no longer occupy the top 20 positions in the IRB World Rankings, but with nine matches over the next seven days there are sure to be plenty more rises and falls as the race for quarter-final spots hots up.
IRB WORLD RANKINGS (as of Monday, September 19):
Last week's positions in brackets -
1(1) NEW ZEALAND 90.55 rating points
2(3) SOUTH AFRICA 86.71
3(2) AUSTRALIA 84.84
4(4) ENGLAND 83.99
5(5) FRANCE 83.78
6(8) IRELAND 82.50
7(6) WALES 80.73
8(7) SCOTLAND 79.12
9(9) ARGENTINA 77.30
10(11) ITALY 73.88
11(14) CANADA 73.74
12(10) SAMOA 73.59
13(13) JAPAN 71.95
14(15) FIJI 71.01
15(12) TONGA 70.30
16(16) GEORGIA 70.00
17(18) USA 66.38
18(17) ROMANIA 65.69
19(20) NAMIBIA 61.24
20(21) PORTUGAL 60.67
21(19) RUSSIA 60.54
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