SYLVANIA, Ohio —

Unfamiliar faces, career-best scores and the world’s top competitors lurking near the lead headlined the opening round of the Marathon Classic on Thursday.

After day one, a new face sits atop the leaderboard at seven-under par. Nineteen-year-old Youngin Chun, a rookie golfer from South Korea finished her opening round with a career-best 64 overall score. 

“I did not know that I shot a 64. The funniest thing is, I shot par on 18,” Chun said. “I saw the leaderboard and there was a seven-under and I was like, 'Who is that?' I asked my dad, 'I think I shot six, right?' And he said, ‘No, you are a seven.’ It was me.”

Chun teed-off on hole 10 and started off hot by birding four holes on the back-nine. She then added three more on the front-nine.

Chun, who is playing in her first year on the tour, is not the only one with the lead. Canadian veteran golfer Alena Sharp is playing in her 15th season on tour and shot a season-best 64 in the opening round.

On Sharp’s first hole of the day she birdied, but then bogeyed on the following hole. She responded with two consecutive birdies and added another on her eighth hole. Her four birdies on her final nine holes are what tied her for the lead.

“I played really well right from the first tee shot. I felt really calm this morning coming into this event,” Sharp said. “I always love playing here. I’ve always kind of done well here, so I have good vibes on the golf course." 

Behind Sharp and Chun, second place initially presented a three-way tie between Germany’s Caroline Masson, Sweden's Jenny Haglund and Toledo-born Stacy Lewis who all finished the day six-under par.

“It’s a great feeling to get off to a good start,” Masson said. “I feel comfortable going out in the morning. It was nice to get a really good round going. I hope to continue that the next three days.”

Haglund birdied on holes 16 and 18. 

“It feels really good, I mean it wasn’t very pretty, but I got the job done,” she said. “A lot of ups and downs. My putting was on point so that really saved my round."

And Lewis, who always has a difficult time playing at Highland Meadows, birdied on holes eight and nine to close out her round six-under. She hit 18-of-18 greens and tied her lowest round of the season.

“It’s a golf course I am not 100% comfortable on. I hit some really good golf shots today, and had some easy tap in birdies,” Lewis said. “I just haven't done that in a long time in general, so I just felt really good out there today.”

But, perhaps the biggest surprise of the day was from Azahara Munoz, who came out of nowhere with a scorching hot finish.

Munoz birded on 17 and then chipped in her shot from 18 for eagle, joining the Lewis-Masson-Haglund trio that finished in a tie for third place.

As the second half of Thursday’s tournament picked up, so did the heat and the wind. Hot temperatures and unpredictable wind gusts made the course play more difficult for the afternoon groupings.

Clariss Guce, a rookie golfer from the Philippines, headlined the second half competitors with a 66-stroke finish, good for five-under par. She finished the day strong with four birdies on the final four holes, registering her best score as a professional.

Guce accompanied Jeongeun Lee6 from the morning groupings in a four-way tie for seventh place. Lee6 shined on the back nine, birding four holes and finishing bogey-free.

Coming as no surprise, Lexi Thompson and Carlota Ciganda, who are ranked number 4 and number 14 respectively in the Rolex World Rankings, were the other two to tie for seventh place at -5.

“I hit it great today. I made some good putts,” Thompson said. “I did not get the breaks I wanted on the last two holes which was unfortunate. It is what it is — that’s golf. Overall, I am pretty happy with how today went.”

Among other notable finishes, Brooke Henderson, who won the ESPY for Female Golfer of the Year Wednesday night and is ranked 8th in the world, finished four-under. She is currently tied for 11th place and feels good about her opening round.

“There’s definitely some lower scores out there this morning but I’m happy,” Henderson said. “I feel like I was hitting the ball well and am putting myself in a good position. Hopefully tomorrow I can make a few more putts.”

Minjee Lee, who’s ranked third in the world, finished one stroke under par. 

Round two will begin at 7:15 a.m. Friday morning. Players will be competing to make the cut and punch their ticket to contend for Sunday’s championship.