You might not have heard or seen these four young Sydney lads before, but 5 Seconds Of Summer have just become the biggest Australian music export since Gotye.

Over the weekend, the Aussie four-piece – all aged under 20 – found themselves at the top of the UK Official Charts as their single ‘She Looks So Perfect’ went #1, making them the first local group to make a UK debut at #1 in 13 years.

The UK breakout follows shortly after similar chart dominance in Australia. Last week, 5 Seconds of Summer became the first Aussie band to score a #1 single in 2014, knocking Pharrell Williams’ ‘Happy’ off of its 11-week perch at the top of the ARIA Singles Chart.

So who are 5 Seconds Of Summer? Well, we’re not going to beat around the musical bush, they’re a pop rock band who’s sound is much closer to the commercial sound of the sonic spectrum than it is the punk. And if you needed any clear indication of their target market, the Sydney band have opened for One Direction on tour.

But before you dismiss them as just another radio-bothering concern, consider that while they may not be your musical cup of tea, 5 Seconds of Summer have quickly become this year’s biggest international success story. ‘She Looks So Perfect’ also hit #1 in New Zealand and Ireland and the EP of the same name is occupying the same slot on the iTunes chart of 49 countries. Their song sales are also matched by ticket sales.

Earlier this month, they sold out a 10-date American tour in under five minutes, as The Music Network reports, and at 2,000-plus capacity arena-sized venues to boot. They replicated similar results in the UK, where they’ve just finished a sold out eight-date headline tour, playing two massive nights at London’s Shepherd’s Bush Empire, and here at home as well.

Shortly after the box office opened last week, 5 Seconds of Summer’s forthcoming tour of Australia – playing two shows at Sydney’s Enmore Theatre and Melbourne’s The Palais – sold out in a matter of minutes, melting ticketing websites in the process.

The huge groundswell for the Sydney boys started online, where the band first went viral thanks to 50 million views on YouTube – with a helpful little push from celebrity fan and One Direction member Louis Tomlinson, who personally plugged the band to his nearly 16 million followers on twitter back in 2012. Since then, they’ve amassed an equally huge presence on social media – including over 2 million followers on both Facebook and Twitter.

Sure, no-one’s going to defend their street cred over bloggable Aussie bands like Jagwar Ma or the grassroots success of Courtney Barnett, but from a commercial standpoint 5 Seconds Of Summer have already surpassed Vance Joy’s budding UK chart success and Tame Impala’s commercial gains in one fell swoop. And they haven’t even released an album yet. Which more than justifies putting them in the same calibre of bands making big waves overseas as much as the long list of Aussie artists that are doing as proud on festival lineups and industry gatherings across the globe.