Lady Gaga, O2 Centre, London<br/>Tim Minchin, Brighton Centre, Brighton

I'm completely gaga for Gaga...and believe it or not, she likes me too (and my hair), which is why I was treated to a special two-hour audience

It's close to midnight, and Lady Gaga is screaming into my face – my face alone, barely further away from me than you are from these words.

Her hair scooped up into a Bram Stoker's Dracula do, wearing bra, knickers, foot-high stiletto boots, a biker jacket and nothing else, the biggest pop star on the planet is serenading me at close range. It's possibly the most surreal moment of mi vida loca so far, and it's not without rivals.

Deep in the bowels of the 02, Gaga has requested the company of five journalists she feels have been supportive or shown an understanding of what she's about. We wait patiently, expecting a 30-second meet-and-greet. Instead, we get a money-can't-buy two-hour Audience With Gaga, including elongated bursts of ultra-energetic, point-blank performance.

When she isn't doing that, she's high-fiving me for my hairdo, getting dry-humped by her fishnet-legged friend Justin Tranter of support act Semi Precious Weapons, and writhing around on a black leather sofa at angles which prove that, while she may have balls of steel, they're only the figurative variety.

In calmer moments, she'll spill beans on Beyoncé and Britney, share a love of Leigh Bowery, read out a touching letter from a troubled British fan who sent her a bottle of Jameson's (we saw it off, it'd be rude not to), and speak articulately about David Bowie – a valid Gaga comparison in so many ways – and her theory that his every incarnation was the result of an on-going dialogue with his audience, a virtuous circle of projection and reflection. Then she'll leap up and start singing at us again, and I'm pinching myself and giggling.

After rolling around the world with The Monster Ball for the best part of a year (the tour will run until at least May), you'd forgive Gaga for being drained and tour-frazzled. Au contraire. She feeds, Bowie-like, off the renewable energy source of 20,000-strong audiences. It's made a monster of her, in the best possible way.

On the surface, the Ball itself hasn't altered much since the opening night in February: dancers who look like warriors directed by Baz Lurhmann, props including an armour-plated New York taxi, hypodermic syringe staircase and subway carriage-turned-sex club, instruments apparently hewn from a volcano, outfits such as "rubber see-through nun", "animatronic ice fairy" and "Red Queen meets vampire bat", and litres of fake blood.

The now familiar hits are present and coruscating: "Just Dance", its Ibiza friendly imperative subtly undercut by the bleakness of the lyric, "Love Game" incorporating the Manson mix, the two Ps ("Pokerface" and "Paparazzi") and, of course, the imperious lion-roar of "Bad Romance", surely the greatest pop single this century.

What's new is the amazing fire whirlwind coming out of the piano lid, and one new song to whet the appetite of anyone a little jaded by the sub-standard "Alejandro" and "Telephone". It's called "You And I", and it's a storming ballad to a lover who "tastes like whisky" when they kiss.

Far from being tour-lagged, she's on fiery form, ranting about her fanbase creating a space for individualism and liberation in a way which would be corny if it wasn't so damn true, reminiscing about being bullied for being uncool and having a big nose, insisting she has never, ever lip-synched in a concert or TV appearance ("Surprise! A pop show ... and the bitch can SING!"), playing the piano with her feet, and making the self-aware boast "I don't know if you've heard, but I've got a very large cock ...."

The best moment comes when she kills Santa Claus, beheading a fan-thrown figurine with teeth and heels, on behalf of the lonely at Christmas. "He was pregnant with chemicals not meant for children," she justifies, surveying the innards.

Tim Minchin – the other eyeliner-wearing, razor-dodging Dickensian-dressed comedian – is the leading Trojan horse of musical comedy, the art's ultimate entryist.

A barefoot count with backcombed ginger hair, the 35-year-old Aussie uses his cuteness – those big eyes, swivelling from side to side, as if scared by his own shadow – to sneak harsh and unpalatable truths past our defences.

Admittedly, in Brighton, officially Britain's Most Godless Town, those defences aren't set too high when it comes to Minchin's refreshingly sceptical perspective. Nevertheless, it's much easier to get away with characterising prayer as "telekinetically communicating with a zombie Jew and asking him to break the laws of physics" when you set it to a rinky-dink bossa-nova beat. Even so, his stunt involving a copy of the Koran has the room gasping.

Then there's "Cont", a cheerful Gilbert O'Sullivan-esque ditty listing bigoted grievances against assorted groups (Muslims on the Tube, breast-feeding mothers, the bi-curious) until it turns out he's lost half the lyrics, and the song's a perfectly reasonable and liberal number called "Context". Clever.

Backed by a full symphony orchestra, Minchin is a phenomenally fast-fingered jazz/blues pianist (and no mean singer), but the words are everything. A throwaway line like, "Your dog has a bigger carbon footprint than your four-wheel drive", reminds me of Richey Edwards in its ruthless candour.

He's at his most brutal when it comes to love, which he compares to a melanoma, and when taking apart the myth of pre-ordained soulmates using statistics, and such sciencey concepts as bell curves, false positives, P-values, confirmation bias and group-think.

You walk out of a Tim Minchin show convinced that everything you ever believed in is meaningless. And, counter-intuitively, that's an inspiring, life-affirming feeling.

Next Week:

Simon witnesses a special Scouse homecoming by Sir Paul McCartney