Montreux is a town famed for its music. Apart from the jazz festival, Deep Purple wrote Smoke on the Water there after seeing the casino catch fire in 1971; a statue of Freddie Mercury, arm aloft, stands by the lake, a tribute to Queen's time recording in the vicinity; everyone from David Bowie to The Rolling Stones to Led Zeppelin recorded here in the 1970s.

The Swiss resort is also known for its thunderstorms: burly clouds, laden with rain and brimming with noise, roll across Lake Geneva with a startling savagery that is amusingly at odds with Montreux’s genteel affluence.

It is July 2014, and at the lakeside Auditorium Stravinsky, a beautiful venue that holds almost 4,000 people, two Mexican guitarists are whipping up their own tempest. Tonight Rodrigo Sanchez and Gabriela Quintero – Rodrigo y Gabriela to most, and Rod and Gab to their friends – are sharing a bill with Robert Plant, a man they worshipped as metal-loving teens. "It's cool," Sanchez says with a nonchalant shrug. "It's cool," agrees Quintero with a dazzling grin. It is a long way from busking on Grafton Street.

“The thing is, we are still an underground band,” Sanchez says later about the hard-graft reality of their supposed meteoric rise. “I think a lot of media, and people in general, are still kind of sceptical about it, because we’re not in big magazines or doing big TV shows. It’s not normal for a couple of acoustic guitarists with no vocals to do this sort of thing. So I get it: I don’t think it’s the type of music to sell millions, so it’s hard to believe. But I think that scepticism works in our favour, because we still have a lot of places to go and still a lot of heads to fill.”

We meet in their hotel lobby before soundcheck, where their tour manager, Carlo Polli, talks about when he started to work with the duo, more than a decade ago. "I met them in Cardiff Airport," he says, "and Gabriela couldn't speak a word of English. But the crowds loved her."

In search of adventure

It’s easy to see why. On and off stage she exudes a bubbly lightheartedness that’s hard to resist. She is likelier to grab you by the hand and regale you about her food co-op in Mexico than she is to make diva-like demands for bowls of blue M&Ms. And she and Sanchez are as warm with their crew as they are with their audiences, greeting guitar techs and sound guys like long-lost friends.

Backstage, in their dressing room, they reminisce about those early days of busking in Dublin, when they arrived in the city from Ixtapa, in Mexico, in search of adventure.

“I have two stories to tell about my life: before Ireland and after Ireland,” says Sanchez. “In Ireland I grew up professionally; everything that I experienced there has changed and shaped the way I am. Without any doubt I can tell you that the first two years that I spent in Ireland were the most amazing years of my life.”

They both credit Niall Muckian, their Irish manager, who has steered their ship since the beginning. "He has convinced us to do things that we would have said no to," Quintero says, laughing. "We call him the third member of the band, because we always take the decisions to him. It's a fine line sometimes when you're in the middle of everything; you get a lot of opportunities, and sometimes it's hard to say, 'Whoah, that looks like a good one.' We always prefer to be respectful of our audience, our fans, our music, and that's the first thing that Niall thinks of."

Things have changed personally for the pair since those early days, too – most significantly they are no longer romantically involved.

“I think it’s the same,” Quintero says of their working relationship. “We’ve got a very good musical bond. I think, musically speaking, it always worked for us. Always. Now we have a very happy friendship,” she adds, with a giggle, “because we are not arguing.”

“I think it has given us more freedom to play together,” Sanchez says. “I feel kind of happier to be on stage without having extra arguments that have nothing to do with music. We’re best friends.”

They leave the dressing room to unwind and meditate before they take the stage. When they do they hook the crowd by their second song. Their playing is fluid and dextrous and thrilling; even a fan with a cast on his arm can’t help but raise it in triumph. Plant may be a living legend, but his set doesn’t ignite the crowd in the same way. Afterwards, as they steep their hands in ice water, they are characteristically understated. “It went well,” Quintero says, grinning. “It was good,” Sanchez says, smiling and shrugging.

A year later I catch up with Sanchez on the phone from his home in Oslo. They have been almost constantly on the road since Montreux, taking in Wembley Arena and Red Rocks, among other venues, along the way. Earlier this year they collaborated with the Norwegian musician Oystein Greni on a Record Store Day release – a cover of Spirit's Nature's Way – and they are now collaborating, albeit remotely, with a number of artists on a new project. "It's just to create music," Sanchez says. "We have some great guests from different genres, and I don't know how or when we're going to release it." Things are constantly moving creatively. Their last album, 9 Dead Alive, saw them shift from Latin influences to the rockier end of the spectrum; the material they are currently writing has – gasp – lyrics. Notes Sanchez has been sharing on Facebook are distinctly heartbreak-hued, a result of a relationship recently ending in Oslo.

“Yeah, they are pretty f***ing sad,” he says. “But, you know, the good thing is that they are really coming from an honest place. We had kind of experimented with some lyrics years ago, but we had trouble with that, because I didn’t feel – and Gab didn’t feel – that what I was writing was honest.

"But when I started writing all of these lyrics, Gab said, 'Now we're talking. It's really coming from what you're experiencing now.' We'd been adding some covers and playing and singing along with the crowd for the past year, like playing Radiohead's Creep and stuff like that. It was kind of an introduction to see how people would react, and it went down very well. So we said, 'Maybe we should write a couple of our own songs and see how they go.'

“We’re not going to change the project or what we are, but we’re just adding stuff so we don’t get bored.”

Guitar Star mentors

There is no time frame for a new album, he says; next year they will concentrate on South America, a territory that, ironically, they have yet to fully tap. Everywhere else they are the spotlight-shunning duo who have gained the respect of fellow songwriters, and their roles as mentors on Sky Arts' Guitar Star talent show, alongside Tommy Iommi of Black Sabbath, among others, are testament to their stature.

“It’s weird,” says Sanchez, “but I suppose we have to accept that we’ve been doing this for the past 15 years or so, and we’ve put a lot of effort into it. People can see from the outside that we’ve had a successful career, and we can’t complain about that. You realise, okay, I’ve earned some kind of place where people get inspired and look up to us.”

I remind him of what he said last year in Montreux, about remaining an underground band despite their arena-sized shows. “Ten years ago it was totally unthinkable, right?” he says. “Last year we played the main stages of many festivals here in Europe. Back then, even for an act like us to play the main stage at five in the afternoon was really unheard of. So I think that’s something good for music in general: non-mainstream music finding a path into big crowds. It’s pretty cool.”

Rodrigo y Gabriela play the Big Top in Limerick on July 13th