With form and confidence on his side, it looks like the 34-year-old is the man to beat for the highly anticipated tournament in the French capital.
Dellien broke his opponent four times in a two-hour, one-minute triumph on Court Simonne Mathieu, capitalising on the former World No. 3's below-par effort.
At Roland-Garros, the world No. 154 defeated Russian Aslan Karatsev 6-3, 4-6, 6-4, 3-6, 7-6 (5) and will now face Canadian Felix Auger-Aliassime.
There are no guarantees in Paris, but Barbora Krejcikova, the World No.2, is thinking long term, as she is back after an elbow injury.
Ramkumar Ramanathan was knocked out of the French Open Qualifying tournament by 18-year-old French player Sean Cuenin.
The French Open administrators have opted not to follow Wimbledon's lead to ban Russian players from competing in the Grand Slam competition.
It was the 35-year-old Gasquet's first victory over a top-two player since defeating Roger Federer in 2005.
Ramanathan has moved on to the second round of the qualifiers where he will go up against France's Sean Cuenin on Wednesday.
Emma Raducanu was forced to withdraw from the 2022 Italian Open due to a physical ailment after she was ousted in the first round.
The French Open is the second of the four annual Grand Slams and it is the only one that is played on a clay surface.