Clinton was glowing about New Zealand's contribution, saying its forces were "highly regarded" and had played a critical role.
"New Zealand's contributions are far beyond what one would normally expect of a country the size of New Zealand."
There has been scepticism about whether the Afghan security forces will be ready to take over when the International Security Allied Forces begin to withdraw next year - but Ms Clinton said the progress they had made was "more a positive story than a negative story."
New Zealand's role in Afghanistan has contributed to the warming of the relationship between New Zealand and the United States over the past decade - it was the first thing Ms Clinton listed when talking about areas of cooperation between the two countries.
Yesterday, Clinton rewarded that effort at a political level, saying Key's leadership had "revitalised" the relationship between the two countries. The US felt "a special kinship, a closeness to New Zealand and the people and we continue to look for our relationship to go from strength to strength."
Key said he had promised New Zealand would stick to its commitment to ISAF - but would "certainly" withdraw in April next year.
The withdrawal, at least a year earlier than Australia and the US, had not disappointed her because ISAF had made it clear they did not want everybody leaving on the same day. "We are on the homeward leg now."
The pair will meet up again in just over a week at the Apec Summit in Russia.