The two acts will now perform at the final where the winner will be decided, and will go on to perform for the Queen at the annual Royal Variety Performance later in the year.
In the third semi-final of 2014 there were more jokes and laughs, as Ant and Dec reminded the judges they were not waiters as Simon Cowell complained about the lack of water on the judges' desk, before David Walliams later made Simon wear an abstract piece of headwear which Amanda Holden took a snap of.
"I can't believe it!" said 24-year-old Lucy, while Yanis Marshall of Yanis Marshall, Arnaud & Mehdi said it had yet to sink in.
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Lucy Kay (top) and Yanis Marshall, Arnaud & Mehdi
Crazy Rouge were the first act with a classy and scandalous burlesque act, and Alesha Dixon called them "a really good opener", while Amanda called the performance, which included the two male dancers removing their shirts, "titillating".
The 12-year-old Bristolian singer Ellis Chick was one act that the judges were looking forward to seeing and he didn't fail to impress them. Wearing a sequin tuxedo, the young boy sang the Ella Fitzgerald classic Cry me A River.
"You're a born little performer", said Alesha although both Alesha and Amanda added that he had some improvements to make.
Ventriloquist Sam Jones gained mixed reactions, with the audience laughing and clapping but the judges looked impressed.
"It wasn't as good as the audition, I was a little bit disappointed", said Amanda, while Simon added: "the material wasn't great", although David admitted how tricky it can be to do comedy on stage.
Alesha's Golden Buzzer act REAformed sang Beyonce's End of Time, and Amanda called it "pretty faultless".
"So much better than the first performance," added Simon.
Brian Chan, who proclaimed he would be a household name, received the first red buzzer of the evening from Simon. The fashion designer's act involved graffiti and models walking down two runways in his designs. "I have no idea what that was", said Simon afterwards.
"The problem is, you know nothing about fashion", joked David to Simon.
Hip-hop dance act Cartel opened their VT with the news that Jamie had left the group following Simon's comments during their audition, but during the performance he returned to big cheers from the crowd. The judges remained split over his inclusion however, with both Simon and Alesha agreeing that Jamie does not fit the look of the group.
The Britain's Got Talent judges
Kitty and Rosie, a mother and daughter singing duo, received positive comments from the judges while 24-year-old opera singer Lucy Kay was told by David that Simon should sign her straight away.
Closing the show were Yanis Marshall, Arnaud & Mehdi, three French men who dance in heels.