Someone must have mentioned to the four remaining acts that last night’s show was kinda important. Without exception, they raised their games and, each in their own way, gave us performances that upped the ante on anything that has gone before in this year’s X Factor. But as Simon was big enough to say after the last song had been sung, there were two acts in this semi-final who were in a different league, and neither of those two acts are his.

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Opening the show this week was young Organ, performing Year 3000 (originally by Busted). After a slightly dodgy start he really got into his stride with this one, and though I hate to say it he actually did a good job of it. He looked amazingly confident and assured, rocking through the number, striding the stage like a boy possessed. I admit, I was shocked. Not only that he pulled it off, but that he & Simon would choose a song which, a couple of years ago, you could hear 7-year-olds the length and breadth of the Mediterranean and Aegean seas singing in holiday-time karaoke sessions. Still, it’s one of the lad’s favourites, so where’s the harm?

Diana followed with her rendition of Avril Lavigne’s Girlfriend and once again I found myself watching with my mouth open. For the first time ever, she looked like a credible artist. With only a single slip when she forgot that it’s important to always hold the microphone in front of your mouth when singing, she panted her way through the song (it’s not really a number you can actually sing) very well, and even managed a few dance steps just to put up two metaphorical fingers in the general direction of Louis Walsh, who was man enough to admit that she’d proved him wrong.

And then? Then we entered the different league. Alexandra’s polished and professional performance of Rihanna’s Don’t Stop The Music was once again world class, even if not quite reaching the breathtaking heights of last week’s Listen. And Rihanna’s music continued to play a pivotal role in the show as JLS followed with an inspiring arrangement of Umbrella. A choice widely regarded as one of those that could have gone either way, the judges were unanimous in declaring it a great success and I had to agree. The boys looked sharp too, in their co-ordinated brown gear.

In the second half of the show, Organ performed Does Your Mother Know by Abba. Another favourite of his, apparently, and he clearly doesn’t care who knows he’s an Abba fan. So again a strange song choice I felt, but he carried it, clearly enjoyed performing, and at least it wasn’t like some of the bland pap he’s been singing in recent weeks.

Talking of bland pap, Diana’s final song was White Flag by Dido. If pushed I’d say this was the performance that final did for her. Because it looked like she was back in her comfort zone, standing still, doing that stuff with her hands and croaking out a lilting, haunting ballad that sounded exactly like every other lilting, haunting ballad she’s given us for the past umpteen weeks. Not saying it was bad, just that for a semi-final and compared to everyone else’s solid performances, it wasn’t even close to being special enough.

And in another seamless segue that brings be to something definitely special enough. To choose Unbreak my Heart was more than a brave move, it could have been suicidal, but as Alexandra said, if there was even a chance that this would be her final song on the X Factor she wanted to go out with a bang. Well the bang was there, no doubt about that, and thankfully she didn’t go out with it. Brilliant. Head and shoulders above any other act in this year’s X Factor and her future is assured whether she wins next week or not.

A predictable choice by Louis of a Westlife number for JLS to close the show: I’m Already There. An assured return to their basics, the lads’ harmonies worked really well in this number, supporting Aston’s lead vocal and bringing back the sound that made them so popular in the earlier rounds. Easily their best performance yet, and the one that prompted Simon to say that they could win the competition, and also to make the comment that, all judges’ partisanship aside, there are two acts in the competition who are in a different league to the rest (i.e. Alex and JLS). That much was surely clear to anyone watching last night.

And so we came to the results (the less said about Il Divo, the better). Did you notice that Dermot mentioned they’d had two million votes? Seems a lot less than in previous years. Anyway those two “top league” acts were put through first, leaving us chanting “Organ, Organ” as we prayed for an end to the weekly misery.

Those prayers granted, I’ve never been happier to be proved wrong (I believed last week that Diana would probably win), and that leaves us with a final between Eoghan, Alex and JLS. Could this be the year of the groups? Will the talent that is Alex win through after three years in the wilderness? Or will the Nana vote hold sway? Tune in for next week’s final at 7.10pm.