STUTTGART, Germany - World No.1 Naomi Osaka was two points from defeat twice in the final set, but pulled off an incredible rally to defeat Donna Vekic in the quarterfinals of the Porsche Tennis Grand Prix.

After leading by a set, Osaka ultimately trailed 5-1 in the decider, but never faced a match point and won five straight games en route to a 6-3, 4-6, 7-6(4).

"I mean I felt like it just happened really fast. She was 3-0 and suddenly, she was 5-1 and I felt like I took a while to get going," Osaka said after the match.

"I didn’t feel like I could swing freely. I think I played the best in the first set, and then it just kind of dipped a little bit, but instead of swinging freely I would say I was trying to be more consistent."

The two hour, 18-minute contest was tight throughout, evidenced by what transpired to see the two players split the opening two sets.

Each woman converted on the lone break point for either player in the set she won, never facing break point on her serve in corresponding fashion.

In the opener, Osaka broke in the sixth game, losing just two points behind her first serve in the set and one point overall in her last two service games, before Vekic turned the tables in the middle set.

Staying even with the World No.1 for the duration by holding her own serve, Vekic sealed a decider with a break in the 10th game, after winning the biggest battle of the match - a four-deuce effort on serve where she had a total of  five game points - to keep her lead in the seventh game.

"I feel like I try not to panic anymore because that takes up more energy and I don't really have that much energy to spare," Osaka nonetheless assessed.

"I just try to think logically and see how I can solve the problem."

After losing five of the first six games of the third set, with Vekic setting the tone by saving two break points of her own to start the decider, Osaka buckled down, and never allowed the 22-year-old to reach match point despite serving for it twice.

Osaka herself even moves two points away from a moral bagel in the decider, only to see Vekic hold on to force a tiebreak, before securing a place in her first semifinal since winning the Australian Open.

"It means a lot I think, especially since it’s clay," Osaka said. "I spent a really long time after Miami just training on clay, trying to get comfortable with it, and I’m really happy that that paid off."