This wasn't exactly a FPTP situation. First, the presidential election spans over two rounds. Second, about a month later, the legislative elections (two rounds also) were won too with a proper tsunami (350 out of 577 seats, providing a governing majority).

When he won the presidential election, everybody thought it was no big deal, as he hadn't shown a single viable candidate to staff any of the 577 seats in the parliament, without which he couldn't wield any real structural power. But he used that weakness as a strength. He hired inexperienced people from all regular ways of life, young and shiny. To the voting public, the message was "you wanted neither left nor right ? Here you go, vote for the almost normal people I'm offering you." This turned into a huge strength, as once in office these inexperienced MP simply followed the group leader, who, you guessed it, was a seasoned politician from olden, and made the parliament a transparent corridor for the presidential power for quite some time.

The public pitch was along the "climb over the left/right stalemate and go forward". But the mechanics, besides good ties with the corporate world, were a masterpiece of perfect timing for every action along the campaign, and then for the legislative elections. In those days I was admiring Macron like you would admire a talented enemy general.