Tears: The 19-year-old was left in a flood of tears as millions of viewers watched her being comforted by host Ant McPartlin and Declan DonnellyJessica managed to get as far as stuttering: 'I didn't choose what I wanted to sing. Apparently, it was somebody...' before choking up and dissolving in tears.
Judge David Hasselhoff however tried to give her some constructive advice, saying: 'You don't have to come out with a whole big production, stay intimate with your audience.
'You did a great job though but go back to what you do best.'
But it was too late and Jessica was bereft.
The show had opened with a Welsh all-girl dance outfit called Dance Angels Elite who dazzled with a colourful routine, and received all round praise, despite some reservations from Simon.
However, there were literally some howlers on the show.
Outright winner: Jai McDowall got the most public votes on tonight's semi-final and was automatically through to Saturday's final
Belting it out: Jai sang a stunning verision the Evanescence song Bring Me To Life
Thrilled: Jai was congratulated by Ant and Dec and said he was chuffed to bits to win through to the grand finalMelanie with Tucker and Twizzle the chihuahuas were Mexican Mayhem - but the dogs failed to perform, to hilarity from the crowd.
However, judges Amanda and Michael were so embarrassed by the act and the fact that they'd put them through to the semis that they ran away from the desk.
After being made to rejoin the panel, Amanda confessed: 'It was absolutely rubbish. I found it endearing and funny first time round, tonight I was excrutiatingly embarrassed. I'm sorry.'
David was left tickled though, enthusing: 'I thought it was the most hysterical act I've ever seeen in my life. You're trying to get them drunk on tequila and you're doing the splits. I thoroughly enjoyed it.'
Jump to it: Telecommunications engineer Steven Hall from Kendal in Cumbria is through to the finals after his comedy dance mash-up
Stirring it up: Some fans were surprised that Steven got through tonight at the expense of other acts on the show
Artist Nathan Wyburn, who had auditioned by making portraits of the judges out of toast and Marmite, failed to impress when his attempt to make portaits out of candles, charred paper and glitter didn't work - and no-one recognised Elvis Presley, Marilyn Monroe or Michael Jackson.
Meanwhile, Amanda - along with many fans - were left shocked after Out Of The Blue - an all-male choir from Oxford - failed to go through after getting one of the best crowd reactions of the night.
They sang a mash-up of Jump by the Pointer Sisters seque into Flashdance (What a Feeling) by Irene Cara.
Hits and misses: David Hasselhoff gives a standing ovation to one of the acts in what was a very varied show - with Simon describing it as the 'most bonkers yet'
On his way: Head judge Simon looked ready for business when he left his London home and headed to the BGT studios for tonight's show with ex-girlfriend Jackie St Claire 
Vroom with a view: Amanda Holden arrived at the BGT studios on teh back of a motorbike againEven Simon had been impressed, saying: 'Guys, after what we've just sat through for most of the evening, thank God for you.
'It's original, different, very kind of Glee-ish and good choices of song, I think you did very well, congratulations.'
Whether or not Simon's criticism affected public voting is a moot point, but when it came to the results show, Jessica had failed to find herself in the top three.
On song: Out Of The Blue appeared to be a big hit on the night, but the public didn't vote them into the top three 
Colourful: But Dance Angels Elite were out of step with the voting public and thus out of the show
Top three: But Edward Hall and his comedy mash-up of children's TV themes lost out to Steven Hall's novelty dance act in the judge's vote
Wonky: Nathan Wyburn's Marilyn Monroe made out of candles was not a hit with the judgesAfter a performance by Jessie J and her new single Mama Knows Best, instead, it was revealed that Scottish singer Jai McDowall had won outright, watched in the audience by Kerry Katona and David's girlfriend Hayley Roberts.
He got the most public votes and was through to the final with his stunning version of Evanescence's Bring Me To Life, which had wowed everyone, and got a standing ovation from judges as well as the audience.
It was then revealed the other two in the top three were effectively comedy acts - telecommunications engineer Steven Hall and his madcap dance moves, and singer Edward Reid, who sang children's TV theme songs to the tune of The Greatest Love Of All by Whitney Houston.
Pout and about: Jessie J, who performed Mama Knows Best on the results show, did her trademark 'salute and pout' look when she arrived at the studio 
Penultimate show: There's just one more semi-final before the live grand final on SaturdayDown to the judges' decisions, three plumped for Steven - apart from David, who went for Edward - and Steven was through to the final and the chance to win £100,000 and to perform before The Queen at the Royal Variety show.
The last Britain's Got Talent live semi-final is on tomorrow night and Simon announced during tonight's show that he was bringing back an act, despite them being voted off before by the judges.
French body popper Michael Moral will now be on the show for a dance-off against fellow hoofer Razy Gogonea tomorrow night in the last semi.
The last Britain's Got Talent live semi final is on Friday on ITV1 at 7.30pm and 9.30pm where the last two acts will win through to Saturday's final - and the chance to win £100,000 and to play for The Queen at the Royal Variety Performance in December.
BGT fans: David Hasslehoff's girlfriend Hayley Roberts (L) and Kerry Katona (R) were both in the audience for tonight's show Britains Got Talent 2011 - Jai McDowall (With Judges Comments), click
Jessie J - Guest Appearance - Britain's Got Talent 2011, click
Edward Reid on Britain's Got Talent, click
Britains Got Talent 2011 - Episode 11 - Semi-Final 4 (Part 1), click
Britains Got Talent 2011 - Episode 11 - Semi-Final 4 (Part 2), click
Britains Got Talent 2011 - Episode 11 - Semi-Final 4 (Part 3), click
Britains Got Talent 2011 - Episode 11 - Semi-Final 4 (Part 4), click
Britains Got Talent 2011 - Episode 11 - Semi-Final 4 (Part 5), click
Steven Hall - Britains Got Talent Live Semi-Final - 2011
Out Of The Blue - Britains Got Talent Live Semi-Final - 2011
source: dailymail