Baltimore rockers Arbouretum follow their Green Man Festival date with a mini tour that takes in a mini venue: Oxford’s Port Mahon. Standing room only, surely.

Please, no encore. Don’t make this go on any longer. Make it stop.

And stop, they do. No encore. Arbouretum get it, and we can get out. RELIEF.

Which is not quite what we were expecting ahead of a gig that, let’s be honest, is a bloody exciting prospect. Listed on the posters as ‘the smallest gig of Arbouretum’s UK tour’, this has to be the rock event of the month bar none. Not even Eels and Nick Oliveri, who are both playing Oxford tonight (sadly not together), can top this one. My mate Si drove all the way over from Cardiff having seen Arbouretum 24 hours earlier in Bristol, declaring it one of the best gigs he’d ever been to. Cardiff-Bristol-Cardiff-Oxford-Cardiff in a day and a half is a pretty conclusive testimonial.

But back to tonight: history is written. Why?

HOTTEST GIG EVER.

Stupid-hot, it is. Pouring sweat and light-headed flakiness all round. The bassist does well to keep his eyes open and stay upright, and the only way to get through this high humidity hell-hole is not to move. At all.

More of this later though ‘coz before Arbouretum take the tiny stage, we have two local bands on the bill – Coma Wall and Listing Ships.

Coma Wall are the unplugged alter ego of the doom-laden Undersmile. They lay funereal Alice in Chains-esque harmonies (Sap/Jar of Flies) over sparse, almost-rustic acoustics and drag it all out at an Earth-paced crawl. A melancholic start for sure.

Listing Ships, by contrast, are all over the place. I mean that in a very precise, right-side-of-muso way – their instrumental math/post rock fusion is krautrock propulsive, bringing to mind Explosions in the Sky jamming on Battles or early-Foals. Or summat. Exhilarating stuff.

We wait for Arbouretum and feel the Ships-generated exhilaration slowly turn to perspiration. Equipment problems delay the headliner’s start and there’s a hint of agitation in the thickening air. Arbouretum look distracted, a bit tense. It’s getting hotter. Finally they start. They get it wrong, it’s a balls-up. They stop.

‘Well, we’ve never done that before,’ says frontman Dave Heumann. ‘You are witnessing a first.’

This error and frank admission somehow breaks the onstage tension and frees them, finally, to do what they came here to do – mesmerise us with their amplified Americana, fluid heaviness and out-there escapism. Arbouretum’s music belongs somewhere earthy and mystical, somewhere without boundaries. It rolls and surges. It’s unhurried but it still rocks. For some reason I start to imagine them playing in a bedouin tent.

But they’re not in a tent. They’re in an airless sweatbox which, by the time the set nears its end, is slowly forcing people out the door before the band call time on their set

Arbouretum still win though. They’re a class act, no doubt about it. We saw that, even if we were too beaten to fully realise it. Bristol next time?