Angelique Kerber, who won her fourth title of the season in Stanford, says she has made some major improvements in her game, but she has to make more in order to beat the best players, especially on her serve.

“I need to play a little more powerful and the second serve, not just pushing and making more spin there,” Kerber said. “I’ve been trying to be more fit, working in the gym, I’m playing more aggressive. I am feeling good and everything is on the plan.”

It has added up to a big turnaround. The 27-year-old is ranked No. 11 and also won titles in Charleston, Stuttgart, and Birmingham this year. The German reached No. 5 back in 2012, when she won her first two titles and reached the Wimbledon semifinals. In 2014, Kerber reached four finals but was unable to win a title. Her toughest loss was against Serena Williams in the 2014 Stanford final, which she led 5-1 in the first set before losing 7-6 (1), 6-3.

Since she brought back her coach Torben Beltz in April, Kerber's results have improved significantly. "I was staying in the moment after I lost the second set, trying to be aggressive, trying to go for it,” Kerber said about her 6-3, 5-7, 6-4 win over Karolina Pliskova in Stanford. “In the third set there were two or three balls for the win. I’m happy I was going for it and not pushing the ball and hoping for the mistakes and that was the key. I have the game and I’m playing tough matches against top players and Pliskova is in the Top 10."

Now almost in the Top 10 once again, Kerber is aiming even higher. “It couldn’t be a better start to the hard-court season, especially in front of the U.S. Open,” she said. “I think I’ve improved a lot mentally. I’m still working on moving on the court. The serve is very solid now—I’m not losing that many games on my serve. I’m feeling confident. Even if I lose some tournaments in the first round, the next one is much better. But I’m not losing too many times in the first round.”

If she keeps this up, Kerber might find herself among the Road to Singapore’s elite eight when the final field is announced for the BNP Paribas WTA Finals. The woman who earlier this year said, “In women’s tennis, there is everything possible,” is quickly discovering just how true that is.