Write a new chapter in the diplomatic handbook. Dedicate it to the off-the-cuff remark – the gaffe, even – which averts a war.

We don't yet know if John Kerry's apparently unplanned comment in London, suggesting Syria could avoid a US military strike by turning over its stash of chemical weapons, has set in train a process that will ultimately prevent armed American action. But Barack Obama described it as a "possible breakthrough" and the relief can be felt across multiple world capitals.

Of course the practical problems are legion – one report claims that getting rid of Syria's chemical weapons stockpile could take not weeks or months but "years". Nevertheless, this latest initiative deserves to be taken seriously because it gives all the key players something they need. Crucially, it would allow the antagonists to step back from the brink without losing face.

For Bashar al-Assad, the prize is obvious. If he agrees to banjax the banned weapons, to use the vocabulary of the Northern Ireland decommissioning process, he can dodge the US bullet that was perhaps coming his way. Even with Kerry promising on Monday that any attack would be "unbelievably small", Assad would still prefer to avoid an American attack if he can.

For Russia, whose foreign minister, Sergei Lavrov, seized on Kerry's rhetorical flourish and turned it into an initiative, there is a double benefit. First, Vladimir Putin gets to pose as the global statesman who stayed the hand of the mighty American hyperpower. Second, Russia has its own reasons for wanting to see Syria's toxic arsenal put beyond use. Moscow has long worried about such weaponry falling into opposition jihadist hands should Assad fall. Spiriting it out of Syria dampens that danger. (Tehran is said to support the latest Russian plan for similar reasons.)

Above all, though, the scheme is a life-raft for an American president who looked to be drowning. All the signs from Congress suggested Obama was heading for defeat, at least in the House, in his quest for approval for military action. Even if he had got it, there is no denying that Obama had long been reluctant to intervene in Syria's civil war by force – for the admirable reason that he could see all the same perils pointed out by his opponents.

Indeed, he only threatened military strikes because he could see no other way both to stay true to the declaration he himself had made a year ago – that the use of chemical weapons would by a "red line" – and to enforce the long-established "norm" against such arms. (It was on these grounds that some of us sympathised with his position.) The latest plan gives him that other way: if Assad gives up his chemical weapons, then Obama can argue that both his red line and the international prohibition were honoured.

Amid the current relief, two points are worth stressing. First, though hardcore anti-interventionists will not be keen to admit it, this breakthrough – if that's what it proves to be – only came about because of the threat of US force. It will be very hard to pretend that Assad would have agreed to such a move under any other circumstances; Russia did not propose it until it suspected American missiles were on the way. For all the opposition Obama's threatened action has generated at home and abroad, that fact surely deserves to be recognised.

Second, there is no reason this initiative should end with the decommissioning of chemical weapons. If the US and Russia can make this scheme work, why can't they work together not just to prevent killing by poison gas but on a diplomatic solution that will end all the killing in Syria? If Iran is, even tacitly, brought into the circle on this process, why not keep that country involved in the wider political negotiation that is surely the only way this conflict will ever end?

Out of a moment of extreme crisis has come an opportunity. Now it's up to all sides to seize it with both hands.