Monfils was spotted in Svitolina's player box during her 6-4 6-1 victory over Viktoria Kuzmova in the second round, leading to an awkward moment when she was asked about it during her on-court interview.
"I didn't really expect to be asked that because I just finished my match," said the sixth-seeded Ukrainian. "We are here for tennis so that's why it was a bit strange."
Svitolina, who previously dated England cricketer Reece Topley, added of the relationship: "He's there for me, he's supporting me, and I'm there for him as well. He understands, I understand, what we're going through. It's great."
Things were not great on court for Svitolina for much of 2018 until the final week of the year, when she defeated five top-10 opponents to win the biggest title of her career at the WTA Finals.
For a player who has struggled to produce her best at the grand slams, it was a timely reminder of what she can achieve.
Svitolina said: "I found my mindset, what I have to find every match, the way I have to act, the way I have to be on a court.
"It's not easy but to be a top player, to be consistently good, you have to always be at the top of your game and that showed me at the WTA Finals that I can do that. I'm always going to try to find this zone where I'm playing my great tennis and I'm there."
For all the talk of the unpredictability of the women's game, the story of the tournament so far has been the top players dominating, and it was the same on Thursday.
Of the first eight matches, all were won by seeds, with Karolina Pliskova and Anastasija Sevastova the only ones to drop a set – the latter doing well to fight off the challenge of exciting Canadian teenager Bianca Andreescu.