Monfils seemed a shadow of his usual self as he opted to follow orders of his new coach, Briton Liam Smith, who endorsed a more composed and focused approach to the match.
But the gamble backfired and Monfils' defeat also ended France's hopes of ending their 36-year wait for a homegrown men's champion.
"It's not the type of match I like to play at Roland Garros indeed. But it's the kind of match that you have to write down. I'm here to win, and when I have a game plan with the coach and a game structure, an attitude, I abide by it," a remarkably calm Monfils, seeded 14th told reporters.
"And of course we are used to seeing me using the audience
a bit more, but with the coach, we decided to do some things differently, to try something else.
"It was not successful. Well, we can say I could have used the crowd more, put more energy, but it's easy to say now."
The plan that Monfils accepted from Smith, who has been coaching the Frenchman since the beginning of 2019, was to stand his ground on the baseline against an opponent who had dropped sets in each of his three previous matches.
"People can tell me what they want, but I was really focused and you don't need to have madness. I was concentrated. I was not able to win the fight, but I was not so far on some points," said Monfils.
"He (Thiem) made less errors. Usually he makes more errors. He gets more, well, angry or excited, and today was a bit less. And when he was getting excited, it was in the court.
"My match was good, but today, to win, I should have played an excellent match and I was not successful. But you should note that I was focused from the beginning to the end."
(Reporting by Julien Pretot; Editing by Pritha Sarkar)
