Operatic duo Jonathan and Charlotte were the first announced finalists, having won the viewers' vote following a stirring performance which provoked a standing ovation from all four judges.
Ballroom dancers Kai and Natalia and singer Paige Turley were also revealed to be within the top three, with the judges' vote eventually falling on the ballroom dancers.
Simon Cowell avoided a second deadlock in a row on the second finalist by sending through Kai and Natalia, after only David Walliams opted for Scottish singer Paige.
Cowell, torn over the decision, said in his final assessment: "I like both. I apologise to the act I haven't put through, I'm going to put through Kai and Natalia."
Alesha Dixon and Amanda Holden were more clearly in favour of the dancers, who admitted to Ant & Dec that they were surprised by the result.
Cascade, Karizma Krew, Graham Blackledge, The Showbears, Four Corners and Michael Fish also exited the competition after failing to make the top three.
Britain's Got Talent continues tomorrow (May 8) for its third semi-final airing at 7.30pm on ITV1.