Their eyes finally met over tax cuts. Both had entered the studio apparently oblivious to each other. There was no eye contact, no greeting.
The impasse isn't broken right through the opening statements and discussions about the brain drain, until the debate turns to tax cuts.
She makes the first serve, noting "John cares so much about the issues of families living on the average wage" that its tax cuts for them were only marginally better than Labour's.
Key returns it neatly, noting "Helen cares so much for the average wage earner" that interest rates in her time have doubled.
She turns toward him, he turns back and the result is not pretty.
Key has made his first interruption early - determined to break the curse of Don Brash, who said after debating the Prime Minister that he hadn't wanted to interrupt because it would be rude to a lady.
John Key has no such qualms. But it takes a determined man to stop Clark in full roar.
Her voice develops into a drone which seems to completely drown out any outside noise.
But he persists. After a while, she adopts the cunning tactic of then blaming him for being so rude as to try to interrupt her.
"You might be used to shouting people down at home, but you're not shouting me down" she booms over him at one point.
But when he starts to talk about New Zealanders being told what size shower heads they can use and which light bulbs, she is quick to return to favour saying she fully intends to "clear that one up right here, right now".
For his part, Key builds up quite a talent for ruining Helen Clark's more fanciful moments.
When she begins to talk about Labour's determination to preserve the world by saving its ice floes and blue seas from climate change, he notes that deforestation has been ripping ahead in the past nine years and coal emissions have grown.
Asked whether the student allowances policy was a "blatant election bribe", Clark starts to reply with the grandiose "I've always had a dream" before going on to talk about the privileges her generation had
John Key happily pops the bubble, noting "my holiday job was cleaning out the chickens".
Silence reigns in the ad breaks. The audience take the chance to fidget. Clark and Key stare fixedly at their notes on the lectern. The only break from this is in the second to last break, when Clark calls host Mark Sainsbury "John" and both laugh.
The next section is leadership. No policies, just her versus him.
When they sense the end is nigh, the relief starts to show. They squabble over who bagged the slogan "better future for New Zealanders" first.
Clark senses the seconds counting down and seemingly out of nowhere starts to call "who do they trust, who do they trust?" over Key, a bid to get that last word in.
When it's over she emerges to declare the debate was a "good old-fashioned debate" and had put an end to any perception of bitterness.