Former French Open junior champion Leylah Fernandez said breaking through on the professional tour was not as easy as fellow teen star Coco Gauff made it look after the Canadian reached the third round at Roland Garros on Thursday.

Fernandez won the girls' title in Paris last year and is now making waves on her main draw debut after taking down 31st seed Magda Linette and 47th-ranked Polona Hercog.

The 18-year-old Fernandez, who captured a first Grand Slam win at the US Open, defeated Hercog 6-4, 3-6, 6-1 to set up a showdown with Petra Kvitova for a place in the last 16.

"I don't think I've changed much. I'm still as energetic and polite as always," said Fernandez, a year after beating Emma Navarro of the US in the French Open girls' final.

"I'm still pretty young and trying to make it as a professional. I'm just happy to be back here, playing on these spectacular courts where legends played."

Gauff, now 16, created a sensation at Wimbledon last year when she became the youngest player in the tournament's history to qualify for the main draw before reaching the fourth round.

The former junior world number one also featured in a high-profile third-round clash against Naomi Osaka at the 2019 US Open before making the last 16 in Melbourne in January.

Fernandez, who is juggling her fledgling tennis career with schoolwork, said Gauff's instant success on the biggest stage was very much the exception to the rule.

"Honestly, it's really difficult the transition from juniors to professional. Coco makes it seems like it's easy but it's hard," said Fernandez, who made her first WTA final at the Mexican Open in February.

"You've got to get used to the pace and keep grinding from 25ks (lower-tier tournaments) to WTA Internationals, finding solutions and keep working hard and try to perfect your game as much as you can.

"Hopefully the results will be there and up to now they have."

Fernandez, born in Montreal to a Filipino mother and Ecuadorian father, credits watching football with her dad in helping with her on-court tactics.

The world number 100 hopes those lessons learned will come in handy in a rare clash of left-handers when she faces Kvitova.

"It won't be an easy match. She's a great player. She went through some difficult times and still bounced back to be in the top 10," said Fernandez.

"I remember watching her winning the Wimbledon championships. The way she played was really inspiring. The way she conducts herself off the court, she's very professional.

"I'm excited and can't wait to play."