To rub it in, Key also observed that former Finland Prime Minister - a right wing politician Shearer had described as "a wise Prime Minister making bold decisions to make his country a better place" - was now a director of the energy company.
But the biggest jousting was over two words: brighter future.
When it comes to political speeches and slogans, a little bit of filching from overseas is inevitable. It cannot be anything as obvious as "I have a dream" or "we will fight them on the beaches" of course. But if the Tasmanian Greens have a nifty line, or Barack Obama pops an aspirational turn of phrase toward the bottom of a speech, why should it not be shared further afield?
Key took great joy in discovering he and Shearer had a joint goal after Shearer apparently inadvertently tried to abscond with National's own slogan of a "brighter future" - the slogan National has used in both its 2008 and 2011 campaigns.
Shearer was foolish enough to use it repeatedly after his own big positioning speech last week.
Key suggested to Shearer that, given National was already following Finland's example by its state asset sales, Shearer could obtain his brighter future simply by voting for National.
Shearer was not alone in catching the Brighter Future contagion. Like bird flu, it has spread far and wide. Last year United Kingdom Prime Minister David Cameron promised "leadership for a brighter future" despite earlier warning that "there are no short cuts to a better future." British Deputy Prime Minister Nick Clegg promised a brighter future for Merseyside after announcing a business fund. China's Premier Wen Jiabao has used it to describe China's relations with, variously, the United States, Russia and India.
Jose Socrates, leader of Portugal's Socialist Party, also used it after winning the 2009 elections. Alas, the future was not so bright for Socrates - he was defeated in a landslide two years later and resigned as leader of his party.
Republican candidate Mitt Romney - undoubtedly inspired by Key's success - is now using it in the primaries. For good measure, he has also mixed it in with part of that infamous Neil Armstrong moon quote, urging voters to "take a giant step toward a brighter future".
US President Barack Obama has also promised "brighter futures" willy nilly - including for veterans and their children, for First Americans and then, lest others fear they are missing out, "for all Americans".
Key has been similarly unselfish about his promise. As well as the brighter future he will bestow on New Zealand, he has said he hoped North Koreans would enjoy the same fate after the death of Kim Jong Il.
Shearer himself appears to have indulged in a spot of line stealing. Of course it could be a coincidence that his speech title of "a new New Zealand" echoed Obama's promise in 2008 that he represented "a new America".
And Shearer's "ready to lead" slogan during last year's Labour leadership contest might only accidentally echo Obama's inauguration speech announcement that America was "ready to lead once more".
Nonetheless, Shearer has shown some flair for the original. Obama might have sung the blues but he is yet to introduce such leadership concepts to the Land of the Free as mango skins, big tents and - most recently - lambs at a circus.