Juan Martin Hernandez believes Argentina can prove Ireland's World Cup scourge once more in a fourth "El Clasico".

Argentina centre Hernandez hailed facing Ireland as a derby to rank right up there with the fierce rivalry on show whenever Barcelona face Real Madrid.

The 33-year-old insists the Pumas can dump Ireland out of a third World Cup in Sunday's quarterfinal in Cardiff, after eliminating the same foes in 1999 and 2007.

Ireland squeezed past Argentina 16-15 at the 2003 World Cup before beating Australia to reach the last eight, but Hernandez believes the Pumas can dish out yet more misery this weekend.

Juan Martin Hernandez scores Argentina's first try© Harry Engels/Getty Images

"I remember in 1999 when we went through to the quarterfinals for the first time," said Hernandez of Argentina's 28-24 victory in Lens. "I was not part of the team then, I was very young but I remember watching on TV.

"These games are like El Clasico, they are derbies. I know Ireland has European teams but for us it has become a nice challenge, a great derby."

Argentina have produced some of the World Cup's most compelling attacking rugby, but Hernandez knows full well the challenge cranks up a notch against Ireland.

He has fond memories of the three World Cup matches in history between Argentina and Ireland, with the Pumas triumphing 30-15 in 2007. 

And Hernandez believes former Racing Metro team-mate Johnny Sexton will be crucial to Ireland's chances at the Millennium Stadium. Sexton is battling to beat a groin problem in time for Sunday's match, with Ireland ready to gamble on his fitness if he is not quite 100 percent.

"He's the most important player," said Hernandez, who will trade Toulon for Argentina's brand new Super Rugby franchise after the World Cup. "He's the one that has the tempo of the team, when they run, when they play, when they kick, everything. He's key to their detail."

Hernandez worked under coach Ronan O'Gara at Racing Metro, developing a new love for the former Ireland fly-half he admitted caught him by surprise. "It's a very good relationship, an awesome relationship now," said Hernandez of O'Gara.

"Before when I used to play against him, you don't hate anyone in rugby, but he was someone you wouldn't like! But I was lucky enough to have him to coach me for one year at Racing, and I discovered a good person.

"All of us know what a great player he was, but I know him more now, and have a great relationship with him. I've asked him if he's coming to the game, and he said maybe. They have a difficult game against Oyonnax I think, so he's not sure."