The far-right leader repeatedly attacked the conservative candidate before he was knocked out in the French race last month but has now appeared to repeat large sections of one of his speeches.
The Front National politician referred to “waiting lists for the Alliance Française [language school] in Shanghai, Tokyo, or Mexico, for the French secondary school in Rabat or Rome”.
The passage - one of three highlighted by French media - was identical to one in a speech made by Mr Fillon in Puy-en-Velay on 15 April.
Ms Le Pen mentioned France's “three maritime borders” with the English Channel, North Sea and the Atlantic, as did Mr Fillon.
She also repeated his description of borders and ties with “Italy, our sister”, continuing: “Then there is the Rhine frontier, the most open, also the most promising - a Germanic world we will yet co-operate with in so many ways, as long as we regain the relationship of allies and not of subjects.”
Mr Fillon had said: “Then there is the Rhine frontier, the most open, the most dangerous, also the most promising - a Germanic world we have been so often in conflict with and with which we will yet co-operate in so many ways.”
Ms Le Pen also evoked the same quote from early 20th century French Prime Minister Georges Clemenceau: “Once a soldier of God, and now a soldier of Liberty, France will always be the soldier of the ideal.”
Footage of the two speeches was posted online by Ridicule TV, a YouTube channel initially set up by Mr Fillon's supporters, before he was eliminated from the French presidential election, having been damaged by a scandal over “fake jobs” awarded to his wife and children.
Florian Philippot, deputy leader of the Front National, said the party “completely owned up” to the similarities with Mr Fillon’s speech amid widespread mockery on social media.
He told Radio Classique that Ms Le Pen's speech was a “nod-and-a-wink” to her former rival’s discourse in order to “launch a real debate” concerning French identity.
Her campaign manager, David Rachline, also played down plagiarism accusations, painting her speech as a form of tribute to Mr Fillon that “was appreciated, including by all of Mr Fillon's supporters”.
The pair shared a number of policy pledges in the run-up to the first round of voting last month, both taking a tough line on immigration, security and Islamist extremism.
Ms Le Pen came second on 23 May and polls predict her to be beaten by the Mr Macron on Saturday, with the centrist candidate expected to win around 60 per cent of the vote.
Additional reporting by Reuters
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies