The 23-year-old continued his breakout year on Tuesday with an assured 6-2 6-2 3-6 6-3 defeat of impressive French talent Ugo Humbert, ranked 84 places higher at No.38 in the world.

Polman's maiden main draw Roland Garros win came despite losing in the final round of qualifying, the last of three lucky losers drawn after a trio of withdrawals on the eve of the tournament.

The win over Humbert was his first top-50 scalp and guarantees world No.122 Polmans at least $130,000.

And it comes on the back of a gutting five-set loss in the first round of the US Open and a second-round appearance at the Australian Open earlier this year, with a long isolation period in hometown Melbourne wedged in between.

"I was just in the cafe waiting, knowing they were doing the (lucky loser) draw but didn't want to watch, I thought it'd be too tense," he recalled of only his second lucky loser call-up in his career.

"The coach watched and I was the last one picked out; very lucky, don't take those for granted, didn't expect to be playing again and now to be the last Aussie standing is pretty cool."

Remarkably, six other Australian men had played before Polmans and lost without winning a set in cold, difficult Paris conditions.

But South African-born Polmans looked far more comfortable than the red-hot hometown favourite as he defied some late nerves in a three-hour, two-minute contest.

Wearing his trademark legionnaires hat, Polmans raced through the first two sets before a gritty hold of serve early in the fourth set sent him on his way.

The Australian hit back-to-back winners for the decisive break before saving break points as he served out the match.

Polmans will play Chilean 20th seed Cristian Garin in the second round, alongside Australian women Daria Gavrilova and Astra Sharma.

Earlier on Tuesday Alexei Popyrin's 6-4 6-4 7-6 (9-7) loss to South African Lloyd Harris marked just his second first-round exit from seven grand slam appearances.

The 21-year-old Popyrin, junior champion at Roland Garros three years ago, ended the match with 20 unforced errors more than Harris and could not manufacture a single break point.

"He served very, very well, I didn't expect him to serve that well," world No.108 Popyrin said.

"I'm definitely disappointed; it's my first time losing for the first time in a grand slam (since his 2018 Australian Open debut).

"I'm not feeling great confidence-wise; I think I'm going to play tournaments until there's no more to play (this year), because I want to get that feeling of winning matches back."

His loss followed comprehensive straight sets losses by Alex de Minaur, Jordan Thompson, James Duckworth, John Millman and Aleksandar Vukic across the tournament's first two days.

HOW THE AUSSIES FARED ON DAY THREE AT THE FRENCH OPEN

Men's singles first round

Alexei Popyrin lost to Lloyd Harris (RSA) 6-6 6-4 7-6 (9-7)

Marc Polmans beat Ugo Humbert (FRA) 6-2 6-2 3-6 6-3

Australian Associated Press