John Key showed he could master policy and presentation in tonight's debate, but he failed to master Helen Clark.

Helen Clark and John Key tonight both got what they wanted–a head-to-head debate without the minor parties. Strategists from Labour and National respectively concluded that this one-on-one format was just what their leader needed and would give him or her the edge. One team of advisers had to be wrong.

With the dust settling on Campaign 08's first television debate, I suspect it's Helen Clark who goes to bed feeling just a little more justified. She was not brilliant by any stretch and would not have won over many who were not already inclined to vote for her. But she reeked authority from decisive smile to her final telling question: "Who do you trust with the future of your economy?"

Viewers would have been looking most closely at Key, the new man. Indeed, Key wanted air-time uncluttered by minor parties so that New Zealanders to get to know him. The man they met tonight was well-briefed, intelligent and articulate. A little nervous at first, but likeable. Willing to take on the Prime Minister, even. But make no mistake, he was the follower. He had the details, but lacked the authority. He repeatedly reacted to Clark's comments, trying to explain her errors or clarify his position, rather than forging ahead with his own; he backed into his answers, beginning his statements with "I'm not arguing against that, but..." or "That's a fair point, but..."; and he let her take-over questions aimed specifically at him. In troubled economic times, Key needed to look like a rough, tough leader and the expert market-man that he is. But for an expert there was little expertise displayed. He failed to offer a laser-like analysis of the credit crisis that made me think, 'yes, he really understands this stuff' and he failed to offer a way out of the current financial mess that went beyond tax-cuts and vagaries about growth. I kept waiting for him to go on the attack, but except for a strong critique of Labour's poor environmental record (an issue that isn't going to win him votes, anyway), he was strangely muted.

For me, the most memorable moment of the debate came towards the end, when Mark Sainsbury, often anonymous as moderator, said that what a lot of people ask him is whether John Key has sufficient mongrel to lead the country. Key needed to bare his teeth and say straight down the camera, "darned straight I do". Instead, he flapped his arms and replied, "That's up to New Zealanders to decide". Sir Robert Muldoon would have been rolling in his grave.

Key did, however, show a mastery of policy. He started especially well, going toe-to-toe in the initial stages when the focus was on his specialty subject, the economy. As the debate went on he hit other highs, hammering Labour on the growth of emissions during their time in government, speaking passionately about literacy and numeracy, and telling how he had written to Clark in 2007 offering to work with her on his concerns about New Zealand's finance companies. Key's people should release the letter, because it showed impressive foresight.

He also showed a good knack for digging himself out of holes. Asked what he would define as "rich" these days, he started by saying it was being "not fearful of the next bill". Hardly a winning line for the middle-classes who may not be bill-shy, but still feel under plenty of financial pressure. But he recovered to speak about his state house upbringing, how it hurts parents not to be able to do more for their kids, and his belief in the "politics of aspiration". Left floundering by Barry Soper's question about previous comments that he didn't take a position on the Springbok Tour in 1981, he admitted to being "mildly pro-tour", but squeezed out of what was an obviously awkward place for him by saying the issues that matter in this election do not involved what happened 27 years ago, but what shape the economy is in in 27 weeks time. Pressed by Sainsbury whether he would be firing public servants to save money, he refused to be drawn, saying instead that "322 people got fired today because our economy is not working". Deft touches all.

Clark smiled for much of the night, but somehow still came off as the tougher one. There were moments when she slipped, however. When Key once spoke over her she tastelessly remarked, "You may be used to shouting people down at home, but...". Later she tried to argue that parents don't really need to pay school donations. Now that's just out of touch. But more than else her greatest weakness was her predictability. With Clark, we've seen it all before and competence is the least that we expect. She would have wanted to make a personal connection with viewers and their everyday lives, to look less aloof, but instead she settled once again for looking like the boss. Not a bad option these days, but not nearly enough to make us long for a fourth term either.

Clark benefited hugely from not having minor parties to deal with. On the environment, for example, she was wobbling. Had Jeanette Fitzsimmons been on stage with her, she may have struggled to fend off both a Green attack from the left and Key's "save the world, but protect the economy first" line from her right. But with only Key to compete with, all she needed to do was assure middle New Zealand that she wouldn't sacrifice growth for the trees. So she played it safe and kicked for the corner, as she did all night. In contrast to Key, she didn't want to look too tough, and while the smile may have grated, she kept her composure.

If voters had low expectations of Key as the inexperienced one, they would have been impressed by a man who wasn't vanquished by a three-term prime minister. But if they had been looking for leadership at a time when their financial security seems to be under threat from market volatility that they can hardly understand, let alone control, then I think the National leader will have left them with more questions than answers.