By Kevin Connolly
BBC News, Oxford, Mississippi
It was the most important single showdown in the most expensive campaign in the history of democracy, so it was bound to begin with edgy, cautious manoeuvring and end with rival claims of victory.
Neither Mr McCain nor Mr Obama was compelling on the economy
And indeed that is exactly how it did unfold - with the spin doctors for Barack Obama and John McCain all claiming that their man had carried the evening.
The aides and advisers spill out into briefing areas within minutes of the end of the debate in the hope of persuading journalists that their side has won.
They know that as soon as a presidential debate is over, very few people will recall the details of dates and places and policy plans which litter the answers of the rival candidates.
Most of us think of it only in the simplest terms - who won? Barack Obama or John McCain?
This debate will be no exception - and there was no shortage of detail in a session which stretched on for about 90 minutes, with the first half-an-hour spent on the economic crisis, and the rest devoted to foreign policy.
So before we review how the rivals dealt with those details - and dealt with each other - here is my answer. It agrees with a quick straw poll I took among the colleagues I followed the exchanges with, but it is my own judgement.
I would say the two candidates finished more or less even on the issue of the economy - and the moderator, Jim Lehrer, even sounded a little frustrated as he tried and failed to get them to address how their economic plans might be changed by the virus of financial decay currently spreading through the banking system.
Both were cautious, neither was particularly compelling.
'Punchy and aggressive'
For a while it seemed it would be the first presidential debate in history when the most interesting question of the evening would be the one asked and answered before the evening's proceedings were under way: would Mr McCain actually turn up?
He had been threatening to remain on Capitol Hill until the two Houses of Congress agreed a response to the Bush administration's proposal for a $700bn (£380bn) federal bail-out fund for Wall Street's tottering Titans.
In the end, though, he was there and in truth it was never likely that he would have stayed away from the most important set-piece political confrontation of his life.
But in the foreign policy section of the debate, it seemed to me John McCain emerged a clear winner, although there were individual issues like Iraq on which the Democratic contender more or less held his own.
The Republican was punchy and aggressive, accusing Mr Obama more than once of naivete, and at one point even saying "Oh please" as he dismissed his opponent's attitude towards dealing with Iran's aggressive rhetoric towards Israel.
You can sum it up with the exchange on the issue of Russia - whose petro-dollar fuelled resurgence as a regional power is going to test the next president throughout his term of office.
Mr McCain recalled looking into the eyes of Russia's Vladimir Putin
Mr McCain was able to describe meeting Vladimir Putin, "looking into his eyes and seeing three letters, K, G and B" - a reference to the old Soviet intelligence agency for which Mr Putin once worked.
Does it sound corny to foreign ears, with a slight B-movie flavour to it? It probably does. I would say in America it plays much better as a tough-guy sound-bite, suggestive of a president who knows how to stand up to Moscow.
Mr Obama's answer on Russia rambled quite a bit and veered off into a dissertation on the need to develop alternative energy sources - not his first of the night.
You could see the logic - Russia is an oil exporter and one of America's biggest problems is dependence on imported oil.
But it felt a little bookish and laboured - you could sense which reply would play better in American living rooms.
Mr Obama had some good moments on Iraq and was able to reel off a series of charges against Mr McCain, finishing each with the phrase: "You were wrong."
And he was generally smooth and businesslike where Mr McCain was spiky and aggressive.
Mr McCain was more spiky in approach than Mr Obama
But the Republican candidate was able to go back to the start of his congressional career in 1983 when America was deciding to deploy Marines to Lebanon and list a huge number of trouble-spots of which he has personal experiences; some were obvious, like Iraq, others rather obscure to most American TV viewers, like Waziristan and South Ossetia.
Foreign policy issues don't decide elections except in moments of grave national crisis, but Americans are electing a new commander-in-chief on 4 November and Mr McCain's people will feel he came much closer to filling that bill than his rival.
The earlier section of the debate on the economy was curiously stilted when you consider that America is currently suffering the worst financial crisis since the Wall Street crash.
At one point, the moderator had to encourage the two men to engage directly with each other instead of addressing themselves exclusively to him.
But their offerings on the economy were standard stuff - familiar to audiences who've already seen them run through more than 30 debates between them since the primary season started.
Mr McCain wants to cut government spending and taxes. Mr Obama wants to do more to improve healthcare and help working families. Neither sounded as they really had a plan to battle the contagion of imminent collapse raging through the financial system.
On that subject, they'll have convinced their own supporters without winning over many waverers.
On foreign policy it all seemed a little clearer, although I should say Mr McCain won on points, without delivering anything remotely approaching a knockout blow.
And it will be some time before it's clear how this evening's performances will be reflected in the opinion polls, which remain generally finely balanced.
There are three more debates to come - two more between Mr Obama and Mr McCain, and one between their vice-presidential running mates, Joe Biden and Sarah Palin.
Expect much more on the economy in those confrontations and, if the polls show that Mr McCain's more aggressive tone has paid off in this first clash, expect all the debates which follow to be a little more bad-tempered and direct than this one.