Ireland beat Wales 35-21 in a World Cup warm-up match to replace the Springboks at No 2 on the rankings.
It is the Irish's highest position since the rankings were introduced in October 2003.
Saturday's match at the Millennium Stadium in Cardiff was played in front of a sold-out crowd, despite the fact that Warren Gatland and Joe Schmidt both used it to test fringe players. Needless to say, the latter will be happier with the depth in his squad.
Ireland scored five tries and could have had a couple more with better finishing, and the final score flattered Wales.
Jamie Heaslip grabbed the first try after a poor pass from Dan Baker off the back of the scrum put Wales under pressure and gave possession back to Ireland. Darren Cave then dotted down following a good Irish scrum, before another Welsh handling error saw Keith Earls sprint away.
Ireland should have scored another first-half try (they blew a three-on-two overlap), but had to be satisfied with a second penalty from Paddy Jackson that made it 25-0. Wales then finally got on the board when Richard Hibbard went over just before the break.
But Ireland reasserted their dominance in the second half, with Simon Zebo getting their fourth try following an attack down the blindside. A great skip pass from Zebo then put Felix Jones away to make it 35-7.
The Irish were reduced to 14 men when replacement Chris Henry was sin-binned for a professional foul, and Justin Tipuric scored Wales' second try while he was off.
The hosts crossed the line again late in the game through Alex Cuthbert, which made the scoreline a bit more respectable.
Wales – Tries: Richard Hibbard, Justin Tipuric, Alex Cuthbert. Conversions: James Hook, Gareth Anscombe (2).
Ireland – Tries: Jamie Heaslip, Darren Cave, Keith Earls, Simon Zebo, Felix Jones. Conversions: Paddy Jackson (2). Penalties: Jackson (2).
Wales – 15 Hallam Amos, 14 Alex Cuthbert, 13 Tyler Morgan, 12 Scott Williams (c), 11 Eli Walker, 10 James Hook, 9 Mike Phillips, 8 Dan Baker, 7 Justin Tipuric, 6 Ross Moriarty, 5 Dominic Day, 4 Jake Ball, 3 Aaron Jarvis, 2 Richard Hibbard, 1 Nicky Smith.
Subs: 16 Rob Evans, 17 Kristian Dacey, 18 Scott Andrews, 19 James King, 20 Taulupe Faletau, 21 Lloyd Williams, 22 Gareth Anscombe, 23 Matthew Morgan.
Ireland – 15 Felix Jones, 14 Andrew Trimble, 13 Keith Earls, 12 Darren Cave, 11 Fergus McFadden, 10 Paddy Jackson, 9 Eoin Reddan, 8 Jamie Heaslip (c), 7 Tommy O'Donnell, 6 Jordi Murphy, 5 Donnacha Ryan, 4 Iain Henderson, 3 Mike Ross, 2 Richardt Strauss, 1 Jack McGrath.
Subs: 16 Rory Best, 17 Dave Kilcoyne, 18 Michael Bent, 19 Dan Tuohy, 20 Chris Henry, 21 Kieran Marmion, 22 Ian Madigan, 23 Simon Zebo.
Photo: David Rogers/Getty Images