Gemma Hayes, Bush Hall, London

A sweet and yearning ingénue

Gemma Hayes is from Ballyporeen, a small Irish village. She's blessed with porcelain skin and the delicate features of a youthful Winona Ryder. Her excellent debut album, Night on My Side, has just been Mercury Prize-nominated, alongside Doves' The Last Broadcast and Bowie's latest effort (she proudly tells us she's just happy to be nominated). This is the last night of her first acoustic tour. It's also her 25th birthday.

From the moment Hayes steps onto the ornate, Edwardian room's tiny stage, she's captivating, and it's not just because of the way she looks. Wearing worn-out jeans, a scruffy hooded top and a black velveteen scarf that seems to jealously guard her neck, she's not dressed to steal the show.

Instead, it's her presence – she exudes a quiet, purposeful confidence – that draws you in. "It's like a wedding reception," she tells the crowd, surveying the grand hall's scattered tables. But she's wrong. With all eyes glued on her, it's like a recital.

But this is not a solo show. For most of it, Hayes's voice and guitar are joined by cumulative accompaniments – sometimes soft and understated, other times a sonic barrage – of a second guitar or bass and (at times over-enthusiastic) drums. So Hayes's decision to open her set alone with the quiet and yearning "Evening Sun", from her 4.35am ep, is a gutsy one. Yet if there are any doubts about her ability to convey the splendours of her sonically rich, layered album without the help of, well, those instrumental layers, they are laid to rest the instant her crisp, dew-fresh voice tears through the expectant silence of the sold-out venue.

It's Hayes's lyrics that stand out, each word writhing with emotion. A new song, "Killing", bleeds with the leave/don't go pain of a broken heart. Her raging current single, "Let a Good Thing Go" is spiked with regret. "Ran for Miles" bursts with the elation of a second chance. To watch Hayes perform these songs at this intimate, pared-down occasion is a treat, and she sings them as if for the first time. We see her flinch, smile and furrow her brow, feeling every aching word and savouring its taste.

Just before Hayes plays what she says is her last song ("Except it's not", she teases, "after this we're going to walk away and the rest is up to you."), her band surprise her with a birthday cake. She cusses them coyly, hides behind her hair and finishes her set. When she's coaxed out for the encore, she's beaming, obviously enjoying something very sweet indeed. And it's not just the cake.