Argentina head coach Michael Cheika played down his half-time team talk after his Pumas team twice came roaring back to stun Wales in the Rugby World Cup quarter-finals on Saturday.

Wales led 10-0 after the first quarter and were 17-12 ahead with 12 minutes to play but Argentina finished strongly with two tries to win 29-17 and earn a semi-final next week against either Ireland or New Zealand.

Argentina looked disjointed in the opening half hour, seeming unable to break down Wales's defence and slow to reorganise their own.

But two late first half penalties from winger Emiliano Boffelli kept them in the game at the break and Cheika insisted he had little to change in the dressing room.

"The first half we made two or three mistakes that cost us a lot, one was the try," said the Australian, who took his homeland to the World Cup final in 2015.

"And then Wales were tactically very intelligent. They played with width, which we didn't expect.

"It took us two or three times to reorganise.

"From then on we were good in defence, apart from the error that led to their try in the second half."

Cheika insisted he was not worried, even during the opening half hour when Wales seemed to be well in control.

"I have experience in these type of games, 10-0 is a lot but momentum is what's important," added Cheika.

"When you get positive momentum you can put quick points on the board and we were always in the game."

Argentina have become a completely different proposition to the team that surrendered so meekly 27-10 to 14-man England in their opening World Cup pool fixture.

But Cheika insisted that was merely part of the building process.

"We knew that first game would be a bit rough and we learnt a lot because there were a lot of first-time World Cuppers in there," he said.

"I don't think there has been some radical turnaround. We just built off what we learnt, tried to be a bit better at the next game."

Cheika said his team had shown one of their major qualities in that match.

"We're starting to get a bit of flow but one thing this team has always got is a lot of fight," he said.

"Even in that game against England we showed a lot of fight, we just didn't handle the occasion that well."

As for whether Argentina can go all the way, Cheika acknowledged that they would not be favourites in the semi-final in Paris.

"We are just thrilled to be going to Paris, we haven't had a taste of it yet at this World Cup," he said.

"We will look at tonight's game and I know we won't be favourites but we'll be giving it our best."

- 'Not perfect' -

Argentina captain Julian Montoya paid tribute to his team's strength of character.

"I think it comes from our personality and the way that we train," said Montoya.

"Nothing has been too easy for us for the last couple of years. 

"We trust each other. We are a very tight group."

Montoya, though, acknowledged that it had not been a perfect performance.

"We know it is not going to be perfect: life is not perfect," said the hooker.

"It's how you embrace the moment and fight for each other. That's what rugby is about."

Argentina will now stay in the tournament right to the end, even if they lose their semi-final against either Ireland or New Zealand, with a third-place play-off awaiting the teams that fail to make the final.

"Two more weeks with this team. I don't want this to end ever," he said.

bc/bsp