Love match: Romance powers Svitolina and Monfils at US Open

Both pushing each other

"We are pushing each other and we are now trying to join each other in the semi-finals," Svitolina said.

"Now it's time for him to step up his game!"

The pair set up a joint Instagram account, which currently attracts close to 100,000 followers, after going public with their relationship at this year's Australian Open.

Svitolina aiming to go past compatriot Andrei Medvedev

Svitolina, 24, credits Monfils with helping raise her game as she looks to translate last year's WTA Finals success in Singapore into a maiden Grand Slam singles triumph for Ukraine.

She is attempting to go one step further than compatriot Andrei Medvedev, who lost the men's 1999 French Open final in five sets to Andre Agassi.

"I think hitting with him, it has definitely helped me to improve my reaction and my footwork, move really quickly," Svitolina said of the impact Monfils has had.

"I think (I'm) more calm, if you want to describe it in few words. It's more calm and I talk more now with my coach. I'm more open with my coach and also with, you know, with Gael about the tennis and my feelings. This really changed, I think, for the past, I don't know, nine, 10 months."

Motivated by 'painful losses'

Monfils watched from Svitolina's players' box as she faced Simona Halep at Wimbledon, although she was blown away by the eventual champion in her first major semi-final after four losing quarter-final appearances at other Slams.

"He's there for me, he's supporting me, and I'm there for him as well," she said during her run at the All England Club. "He understands, I understand, what we're going through. It's great."

Svitolina faces Serena in semi-finals

Svitolina will have another chance Thursday to reach her first Grand Slam final, and she believes lessons learned from past failures have prepared her to take the next step.

"I had some tough matches round of 16, quarter-finals before I started to win them. I think it's been tough and painful losses sometimes, but I think they gave me this push, this confidence and maybe helped me in some matches," Svitolina said.

"I don't think that I was expecting going into this tournament that I'm going to make semis. I'm just taking one match at a time.

"It's a Grand Slam. There is lots of pressure. You have to just go out there, do your job and don't think too much what's going on around you, and who handles it the best wins."

The Ukrainian will face 23 Grand Slam winner Serena Williams in the semi-final. Williams powered into the last four of the US Open with a crushing straight-sets quarter-final win over Wang Qiang that marked her 100th at Flushing Meadows.

On facing Serena in semis

Svitolina, set to climb to at least third in the WTA rankings after her performance here, will be up against Williams, who is seeking a 24th Grand Slam crown to equal the all-time record held by Australia's Margaret Court.

"Definitely it's a big challenge to play against her. I mean, doesn't really matter who I'm going to play in semi-final. It's a challenge," Svitolina said.

"Person who reaches the semi-final is playing well. It's something that you have to bring your best game to beat them."