How millions of YouTube hits and a phone call from Elton John rocketed two classically trained cellists to stardom.

Croatia’s got talent. And two childhood friends from Zagreb, Luka Sulic and Stjepan Hauser, have set out with their cellos on their backs to show the world just how far raw talent can take you in the age of YouTube.

The pair, playing together as 2Cellos, boasts serious classical credentials: Sulic studied at London’s Royal Academy of Music and has given concerts at Wigmore Hall; Hauser has racked up 21 first prizes in international cello competitions and includes two performances for Prince Charles among his career highlights.

But it was with a video of their two-cello arrangement of Michael Jackson’s Smooth Criminal that the boys found fame: within days of its appearance on YouTube, their self-made clip had gone viral. Sony Masterworks came calling; then, out of the blue, so did Elton John.

“After he saw the video he phoned us personally,” Sulic recalls in thickly accented cantabile English when we meet at the harbour-view Sydney hotel where he and Hauser are staying. “He said he loved the video as well as our classical performances, and invited us to tour with him.”

The rest is a YouTube fairytale: 2Cellos has opened for Elton John and joined his 11-piece band throughout Europe since June, and plays in the Australian leg of the tour until December 11. “He’s a great artist, a living legend,” Hauser says of the veteran entertainer who recognised the duo’s talent (and marketable good looks), “but at the same time so supportive and generous.” As with their playing, the young men are so attuned to one another that they keep finishing each other’s sentences and it becomes hard to get a complete quote out of either one.

Playing an electric cello to 30,000 people in a stadium is a far cry from the genteel intimacy of Wigmore Hall, but Sulic is enjoying his newfound rock-star status. “There are screaming girls, a light show… As a cellist you never imagine you will play this kind of event. That’s a special feeling.”

Sulic is realistic and grounded about what crossover repertoire like Coldplay, Muse and Nirvana has done for his career. “Before, we played for five people clapping in a recital hall!”

Hauser agrees that they had “the energy for a whole stadium and felt a bit restricted playing only in small venues”. Although he has respect for the classical cello repertoire, “you can’t make it big with Schnittke and Britten sonatas.”

Elton John’s slow ballads – Sorry Seems to be the Hardest Word and Don’t Let the Sun Go Down on Me – may be ideally suited to the innate lyricism of their instrument, but it’s the high-octane energy of the duo’s own arrangements, and the sheer vigour and athleticism of their performances, that has made 2Cellos favourites with the crowd.

“People don’t know what the cello is capable of – this is what we wanted to show,” says Hauser. “By playing only classical pieces you can’t really discover all the possibilities of cello. The notes have been written for hundreds of years; you can’t improvise, you can’t expand techniques. Now we have the opportunity to do anything we want, and for energy and adrenalin nothing can compare.”

I ask Hauser, the last student of Rostropovich, what the Russian master cellist would have thought of the 2Cellos project. “He’d love it! He was also a crazy guy. He launched a cello revolution, expanded cello repertoire, making people write more music for cello.” Rostropovich was, incidentally, a great friend of Elton John.

Sulic adds, “He was a humanitarian, he lived through Communism, the fall of the Berlin Wall. But you cannot change the world with Shostakovich anymore; those times are over. We are doing what the new generation wants.”

Hauser insists that rock is as fulfilling as classical music – perhaps even harder to play – because “we use all our virtuosity to the maximum extent.”

“You have to imagine that there’s just two of us and two cellos and we have to play for 30,000 people and achieve the sound of the whole band on just two instruments,” explains Sulic. “So our arrangements have to be demanding, hard, interesting. I tune my cello differently. We can achieve the intensity of the whole orchestra with just two instruments, which is very unique.” Eschewing “cheesy arrangements”, they strive to keep their sound as “authentic” as possible.

The lads admit they came late to rock after growing up with classical music, but Sulic sees it as a firm advantage. “Our ears are fresh and we developed the sensitivity that classical music delivers and that helps us in choosing the right songs for our instruments.

“The songs we love, U2 and Sing, these are the same as classical masterpieces. You cannot say one is worth more than the other.”

Hauser, too, believes that “one song from U2 might have the same emotional power as a Chopin Polonaise.”

The boys have introduced some classical music into their set for Elton John, each playing solo pieces with piano accompaniment by composers including Tchaikovsky, Debussy, Piazzolla and even Ennio Morricone. To Hauser’s delight, the audience “love it as much as they love the other stuff. You educate them as well – they go out and look for this music.”

“And then we join together for Guns N’ Roses!” Sulic grins.

Read the Limelight review of 2Cellos’ debut album.

2Cellos open for Elton John in Brisbane, the Hunter Valley, Melbourne, Adelaide and Perth until December 11.