That semi final game, on May 3rd, 2009, will forever be remembered for the dramatic conclusion to a pulsating clash. Drawn at 26-26, and no winner found after extra time, a penalty shootout was required. Few have forgotten the Williams failed attempt which sailed wide to give Leicester the win.
"I had cramps after more than 90 minutes of a very hard game," recalls the 29-year old prop on one of his many visits to the Millennioum Stadium - where he will return with Los Pumas when they tackle Wales on August 20th in what will be Argentina's sole test-match of the year before Rugby World Cup.
Ayerza, a Leicester resident since 2005 and a much loved member of a front-row that includes his fellow countryman yet Italian prop Martín Castrogiovanni loves the iconic stadium in the heart of Cardiff..
"Certainly it is one of the greatest stadiums in the world and coming here you always know you are in for a hard game. From the moment you arrive in Cardiff you know that it is rugby full on."
The last time Los Pumas were in town, in 2009, the Tiger prop recalls: "The roof was closed and the noise level was incredible. You can't avoid the adrenalin rush, but it is something you start feeling much earlier.
"Very quickly you understand the passion Welshmen have for rugby and that will certainly be the case when we play them in a few week's time."
Los Pumas are back in the country after a two-week camp in Pensacola, USA. Forty degree temperatures were the norm as they worked hard on fitness in a high tech high performance institution. Their first training session in the outskirts of Buenos Aires was in 4 degrees.
"We are not supposed to peak for the Welsh game as everything is geared to our debut in Rugby World Cup, but we will certainly be ready for a huge challenge," said Ayerza.
"We came here in 2007 on our way to France and lost and in 2009 we were very well beaten. We certainly want to play good rugby in our only Test match of the season," he added.
He has mostly good memories of the Millennium Stadium, thanks to his forays with Leicester Tigers. "Not kicking in that game against Cardiff Blues was something I'll always remember! I hope when we play Wales is another one."