NEW YORK • As Elina Svitolina advanced to the US Open semi-finals on Tuesday, the other half of tennis' super couple watched intently from the front row of her player's box.

Svitolina, the Ukrainian fifth seed in women's singles, and Frenchman Gael Monfils, No. 13 on the men's side, have been dating since late last year, and they are both flourishing in New York, making their most successful joint run at a Grand Slam.

"Definitely we are pushing each other, I think," Svitolina said of Monfils in her on-court interview.

"We were trying to join each other in the quarter-finals; now, it's the semi-finals for him. Now he needs to step up his game."

Monfils, 33, played his quarter-final against Italian Matteo Berrettini yesterday, seeking to make his third appearance in a Slam semi-final and his first since the 2016 US Open.

The result of the match was not available at press time.

Svitolina, 24, reached her second consecutive Slam semi-final by beating Johanna Konta 6-4, 6-4.

A few hours after that match, Monfils and Svitolina did a joint interview on ESPN.

They had already gone public on social media, engaging fans on a joint Instagram account named "Gems life", playing off their initials.

It currently attracts close to 100,000 followers.

"Social media is a big part of our job," Monfils said on ESPN, explaining that the impetus for creating the account was to exert control over revealing their relationship.

"The idea came from him more," Svitolina said in an interview earlier this year, laughing. "He's very creative, so we were talking about it, and he came up with 'Gems'."

The two post to the account frequently, sharing photos of themselves together and also of reactions to each other's matches.

However, the account was seen to be "frozen" in June, contributing to rumours of a break-up. But Gems resurfaced before Wimbledon and the duo were back on court and training together.

They explained then: "We just had some time for ourselves, you know. I think we needed a little space.

"It's cool to share with the fans but the last two, three weeks we were out of ideas. But the thing is after everyone said we break up, we were like 'OK, OK let's put it back!' And then we have fun."

Svitolina said: "Of course when we go on the court we are very focused on what we have to do.

"But that's only a couple of hours a day, and in the end we have an off-court life. People are very curious how that's going, so for us it's not a problem to share. We're just happy that most people like it."

She has been practising with Monfils throughout the tournament; his powerful shots, she said, have prepared her well for the attacking players she has faced in the draw, including Konta and Madison Keys.

In the semi-finals today, Svitolina will face perhaps the biggest hitter of all: eighth-seeded Serena Williams, who needed just 44 minutes to defeat 18th-seeded Wang Qiang 6-1, 6-0.

Monfils, whose career-high ranking peaked at No. 6 in 2016, has advanced 20 spots so far this year to 13th, an improvement many have credited to Svitolina.

She is seen as quiet, serious and reserved - characteristics she attributed to a stint training in Kharkiv, Ukraine.

Monfils, raised on the French Caribbean island of Guadeloupe, is jovial and exuberant, one of the more charismatic players on tour.

He said in the ESPN interview that Svitolina has brought "more discipline" to his game.

"She is a hard worker, very professional," he said. "Sometimes too professional, I think. Because there has to be a balance. Definitely I bring a little bit more joy to her, but she will bring me more discipline as well."

Svitolina added that despite the differences in their approach to certain things, they understand each other "really well".

Earlier this year, she joked that she did not want other players to create competing couples accounts.

"We'd like to be No. 1 at something at least," she said.

"We're not in tennis, yet, but for couples, I think we are."

NYTIMES