Lorde is continuing her rise to global stardom, retaining her place at the top of the US singles charts and performing on one of the world's most popular chat shows.
The Kiwi singer extended her lead over Katy Perry's Roar to stay atop the Billboard Hot 100 for a second straight week.
Royals was 19 per cent bigger than Roar, based on a measure of digital sales, radio play and online streaming, Billboard said.
It was less than one per cent ahead when it rose to the top of the chart last week.
Lorde is also in the hunt for a US number one album.
Her full-length Pure Heroine sold 129,000 copies to debut at number three in the Billboard Top 200 album chart, behind Justin Timberlake's The 20/20 Experience, 2 of 2 and Drake's Nothing Was The Same.
The 16-year-old singer had just delivered a smokey-voiced version of Royals on the US chat show Ellen when her chart placings were announced.
Her performance earned praise from host Ellen Degeneres, who took to the stage to declare her love for the artist.
"Our next guest is only 16 years old and has the number one song in the country. When I was 16 my best friend was a blanket named Tammy," she said.
Degeneres later posted a photo of Lorde's performance to Instagram, with a caption saying she was "incredible".
Meanwhile, Lorde has scored a prominent spot on a global Samsung commercial.
Royals is the soundtrack for Samsung Galaxy ad The Developer, which features soccer superstar Lionel Messi.
The song's placement was negotiated by Lorde's label Universal and Sony, who represents her producer and co-writer Joel Little, Billboard said.
The commercial's creators were originally going to use a show tune before opting for the hit song, it said.