When it comes to tennis it seems love does not conquer all as Gael Monfils discovered on Wednesday when he failed to follow girlfriend Elina Svitolina into the semi-finals of the US Open.

Svitolina will go it alone into the last four at Flushing Meadows but boyfriend Monfils will be cheering from the players box on Thursday when she faces local favorite Serena Williams, who is chasing a record equaling 24th career Grand Slam title.

"It's going to be definitely a tough match for her," said Monfils. "She has nothing to lose. She knows Serena well. She knows the crowd is going to be against her.

"It's going to be a tricky one at the beginning, I would say, for both.

"I think it is important for Serena to come out fast because if she should come in slow, I think Elina will be there."

Until Monfils's 3-6 6-3 6-2 3-6 7-6(5) quarter-final loss to Matteo Berrettini, the charismatic Frenchman and Svitolina had been putting a new spin on the Grand Slam love story penned when Andre Agassi and Steffi Graf won the French Open titles in 1999, although at the time their burgeoning relationship was a secret.

Svitolina and Monfils have been together for over a year but their romance has captivated even the most jaded New Yorkers during the US Open.

While they have not shouted their devotion from the top of the Empire State building neither have they tried to hide it and they routinely post photos on social media, including an Instagram account they share.

In contrast Agassi and Graf went to extremes to keep their relationship secret with the German watching Agassi from the bleachers at the US Open so as not to spark rumors.

While Monfils' and Svitolina's relationship has blossomed, so have their respective games.

Svitolina, who trains with Monfils, has now made it to the semi-finals of the last two Grand Slams and credits the Frenchman for improving her ability to handle big shots and bigger expectations.

"He's hitting pretty strong and very heavy," said the fifth seeded Ukrainian. "So I think definitely it helps me to practice with him.

"I think hitting with him it's definitely helped me to improve my reaction and my footwork.

"I think I am more calm, if you want to describe it in few words.

"I'm more open with my coach and also with Gael about the tennis and my feeling."

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