Fans in quirky and glittery outfits waved flags from the participating countries inside the arena on Tuesday, with many dressed up as their favourite contestant or in their national colours.
Croatia's Baby Lasagna (real name Marko Purisic) and Ukrainian duo, alyona alyona and Jerry Heil, are both among bookmakers' top five together with Italy, Netherlands and Switzerland to win the music kitsch-fest.
Streaming data from Spotify also suggests a strong chance for host nation Sweden.
"For Ukraine this is a big platform ... I think this is the place where you can state your mind freely, openly and for the world to listen," Ukrainian fan Victoria said, as she arrived ahead of the show.
Ukraine's folk-inflected pop song Teresa & Maria, which has a strong dance beat and fast-paced rap, is about union, kindness and love, as well as the resilience and strength of women, according to its performers.
Eurovision fans Ross Stewart and Ivo Vasilev from Britain arrived ahead of the show dressed as Croatia's Baby Lasagna.
"We tried to recreate it with what we could buy off Amazon. So we decided, because he's performing tonight, to dress up as him," Stewart said.
The artist's entry Rim Tim Tagi Dim is about a young Croatian who leaves his home aspiring to become a "city boy" with better opportunities.
Security was high around Malmo arena, but police said the evening went as planned.
Cyprus, Finland, Ireland, Lithuania, Luxembourg, Portugal, Serbia and Slovenia also advanced to Saturday's grand final.
Former Eurovision contestant Eric Saade made a guest performance with a black and white keffiyeh scarf wrapped around his wrist.
Eurovision bills itself as a non-political event and organisers have resisted calls to boycott Israel from this year's competition, sparking protest from artists and ministers.
Much focus is expected to be on Israel's Eden Golan and her song Hurricane in the second semi-final on Thursday, with bookmakers placing her among the top 10 to win the competition.
