Raonic, the No. 15 seed from Thornhill, Ont., had 24 aces in the 7-5, 3-6, 7-6 (3), 6-2 victory on the Lenglen showcase court at Roland Garros.
"It was a difficult match," said Raonic, who improved to 4-0 lifetime against Llodra. "Mica's not just tough for me to play, he's tough for everyone.
"I'm very content with my tennis, I played well today. My serve is the most important part of my game and it worked well today. When it does that, I always play better."
Raonic will next face big-serving South African Kevin Anderson, who beat Russian Evgeny Donskoy 6-7 (8), 6-1, 7-5, 6-2.
Raonic recorded four breaks in 12 chances against Llodra.
"He does a lot of things to make you feel uncomfortable," Raonic said of the local favourite. "I felt like at one point I just let it get too much, we were playing under his terms rather than mine. In the first set I created a lot of opportunities for myself, especially on his serve."
"It was a good match," he added. "I won but I wish I could have gotten going a little bit better. But fortunate in that tiebreaker when I felt like my back was up against the wall, I got going and sort of carried that through the fourth set."
Also Wednesday, qualifier Vasek Pospisil of Vancouver dropped a 7-6 (9), 6-4, 6-7 (4), 2-6, 8-6 decision to Argentina's Horacio Zeballos in a match that lasted over four hours.
The match began late Tuesday but was suspended due to darkness in the fourth set. When play resumed, Pospisil took the fourth set and moved up a break at 4-2 in the decider only to give up a break a game later.
Zaballos, who beat Rafael Nadal in February on clay in Chile, later broke for a 7-6 lead and held serve for the win.
"It was very disappointing," Pospisil said. "I was up 4-2 and completely (gave) him three points in the next game. It was so unlike me. I'm hardly likely to give a break back, especially after fighting so hard to get into winning position.
"I came from two sets down against a good clay player, It was still a positive match for me. My game has been improving a lot. Maybe my head was not ready to win a match like this. Maybe my game is improving faster than my head is ready for."
Pospisil was looking for his second career victory at a Grand Slam. He won a first-round match at the U.S. Open in 2011.
In men's doubles play, Toronto's Daniel Nestor and new Swedish partner Robert Lindstedt came back from an early 2-5 hole for a 7-6 (8), 7-6 (4) first-round win over Russian Mikhail Youzhny and Sergiy Stakovsky of Ukraine.
Nestor is a three-time defending champion and holds four French Open trophies overall with three different partners.
He has a 7-4 record with Lindstedt since they first teamed up last month.