Russia's Tolmachevy Sisters were booed in Copenhagen as they qualified for the final of the Eurovision Song Contest.
The 17-year-old twins initially received a warm reception for their song, Shine, at Tuesday's semi-final.
But when they progressed to the final, some sections of the 10,000-strong audience expressed apparent disapproval of the Russian artists.
Experts have said Russia could suffer at Eurovision over the crisis in Ukraine and its stance on gay rights.
Nine other countries qualified for the final on Tuesday, including Ukraine's Mariya Yaremchuk, whose performance was enhanced by a dancer running in a giant hamster wheel.
San Marino made it through for the first time ever, marking a personal victory for singer Valentina Monetta, who has been kicked out at the semi-final stage on two previous occasions.
Montenegro will also make its debut in the final, thanks to singer-songwriter Sergej Cetkovic, whose ballad Moj Svijet has echoes of Celine Dion's My Heart Will Go On.
The oddly-named Aram Mp3 eased through for Armenia. His song Not Alone, which begins as a simple piano ballad before spinning off into dubstep, is the bookies' favourite to win on Saturday.
Other hotly-tipped songs by Sweden, Hungary and Azerbaijan also qualified alongside less-favoured tracks from The Netherlands and Iceland.
Latvia's novelty act Aarzemnieki were kicked out after their song Cake To Bake ("mix some dough, add some love, let it bake") failed to impress.
The next 10 qualifiers will be selected at the second semi-final on Thursday night.
Last year's winner, Denmark, is already guaranteed a place, alongside the "big five" nations who financially support the EBU, which organises the annual contest: Germany, France, Italy, Spain and the UK.
The UK's entrant is Molly Smitten-Downes - a newcomer who was selected through the BBC's Introducing scheme for unsigned acts.
It is hoped her song, Children Of The Universe, will fare better than the UK's previous two entries. Bonnie Tyler placed 19th last year, while Englebert Humperdinck came second from last in 2012.
Her single entered the UK chart at number 48 on Sunday, and is expected to break the top 40 after Saturday's final.
Bookmakers' have upgraded her chances of Eurovision victory over recent weeks - she currently stands in the top five with odds of 6/1.
The 27-year-old joked she would "trash the green room" if her song got "nil points" from the jury.