Wide Awake is the hottest ticket in town with Caroline Polachek, Viagra Boys and more

The day kicks off in the shade of the Moth Club/DMY tent, where Montreal's Cola are bashing out art-punk jams for the early birds. Frontman Tim and bassist Ben cut their teeth in Ought back in the day, but their new tunes are jumpier and more upbeat, somewhere adjacent to Parquet Courts or 'Men's Needs…' Cribs. Their leather jackets may not stay on for long, but they're just as slick as their performance.

A hop over to the Windmill/So Young stage finds newcomer Gretel Hänlyn taking techy diffs in her stride to deliver the first 'wow' moment of the afternoon. The Mura Masa protégée delivers a rougher set than her glossy recordings would have you believe, but in all the right ways - joined by a three-piece band, the frenetic energy from cuts like 'Drive' and 'Motorbike' is irresistibly joyous. Her vocal ties the whole thing together, moving from gloomy lows to lofty highs with ease, and as she lurches into glistening love song 'Today (Can't Help But Cry)', stars align: its sugary optimism is the stuff music festivals memories are made of.

The schedule boasts a ton of alumni from the now iconic Brixton Windmill, barely a kilometre away, but the band who come out at the front of the pack is unquestionably Jockstrap. The Moth Club tent is rammed and stifling when the duo arrive to showcase last year's debut 'I Love You Jennifer B', in the day's most enthralling hometown victory lap. When glitter-clad Georgia Ellery announces, "It's time to dance", she's not kidding; a bombarding remix of Debra has the crowd wrapped around her finger where they remain through pivots to folky anthems ('Glasgow') metallic tearjerkers ('Concrete Over Water') and back again; when '50/50' hits its climax, there's not a body stood still. When they bounce joyfully off stage, Taylor Skye giving the front rows a good soak with a water pistol en route, it's as though a fraction of their 40-minute slot has passed.

With the sun clipping the treeline and those £8 canned mojitos working their magic, who better to usher in silly hour than Viagra Boys, who make light work of turning the main arena into a sea of bouncing mullets and dust? The six Swedes are wickedly tight for a group who look like they met on a night bus and decided to form a band. Breakout hit 'Sports' is the highlight, frontman Sebastian Murphy popping his joggers off for some golden hour pushups in his boxers in its closing fold, obviously.

And then it's time for Caroline Polachek to make her festival headline debut. It's only been a few months since her Valentine's Day special at London's Eventim Apollo, so tonight's show is much the same, but as Caz welcomes Wide Awake to her island, the sense of occasion is potent. Who else could get an entire festival audience to applaud "the beautiful half moon" hanging in the sky? She twists and turns around the scenery-bedecked stage, the ever-catchy 'Bunny Is A Rider' breathing new life into the pink-eared audience; sweeping through chapters of 'Desire, I Want To Turn Into You' she has Brockwell Park in the palm of her hand. Sunset brings an apt vigour to the show, 'Ocean Of Tears' a lush noise spell, and 'Fly To You' echoes of the choppy breakbeats that continue to rumble away in the background of the festival's other stages. Her illuminated backdrop shifts from desert to jungle to gilded dome in turn with each fold and, while there's the odd lull, the set is never not impressively choreographed, Caroline's playful stage demeanour a treat to behold. 'Smoke' is the set's apex - its irresistible na-na-na's are enough to hook in any passersby for whom this may be their first encounter with our Caz - but the pure pop gem that is 'So Hot You're Hurting My Feelings' is the obvious crowd pleaser. When the lights come up, and the bus queues build, it's the one the masses continue singing down the street, a magical end to a day that's been honestly So Hot.