For Ana Konjuh, her well-earned upset victory over Agnieszka Radwanska late Monday night was redemption — in two ways.

At Wimbledon this year she held three match points against Radwanska, then sprained her right ankle by stepping on a ball trying to get to a drop shot. She lost 9-7 in the third set of the second-round match.

In early 2014 she had surgery on her right elbow and missed several months. This was after she won the 2013 U.S. Open junior title. Then this year she has had a back issue and the sprained ankle.

Overcoming it all, the 18-year-old is now in the quarterfinals of the U.S. Open. The talented Croatian was thoroughly convincing in beating the Open’s fourth seed and the only player besides Angelique Kerber who could have unseated Serena Williams as the No. 1 player at the end of this tournament.

Konjuh served first, lost it, and Radwanska never came close to breaking her again in the 6-4, 6-4 win. With a serve that reaches 118 mph, a forceful forehand and a blistering backhand, Konjuh (pronounced Kon — juh) looks as if she belongs at Ashe Stadium, where she will face Karolina Pliskova on Wednesday.

“She’s an incredible player, and I’m just happy to have the opportunity to play her again,” Konjuh said of Radwanska. “This time I got the revenge, so I’m really happy.”

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Konjuh’s serve produced six aces and three service winners and her groundstrokes piled up 38 winners. She continually stretched Radwanska from side to side, a player who generally thrives in that game, but was left befuddled.

“I’m real excited about my performance tonight,” Konjuh said. “My serve was pretty good tonight. I don’t think she had any answers.”

Health concerns have dogged Konjuh, though perhaps the vitality of youth has helped her heal quickly.

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“I had a few health issues. I had my back. Then I sprained my ankle with Aga in Wimbledon. I was out for like two or three months,” Konjuh said. “That’s kind of had an effect on me. I’m still young. I still need to experience things. I think I didn’t have that many matches as I should. It was tough to come back every time. But here I am in the quarterfinals of the Grand Slam, so I cannot complain.”

Radwanska couldn’t help but be impressed. “She’s really making good angles in the rallies,” she said. “You go from very far from the court, then she have open court. That’s dangerous. She makes good angles from both sides, and of course good serve as well. That makes it really dangerous opponent.”

A dangerous opponent for anyone who seems entirely comfortable with where she is, in New York City, in the U.S. Open, at Ashe Stadium.

“It’s really a privilege for me to be here, just playing for the finals,” Konjuh said. “I’m 18. I won the juniors here. I have good memories. I love the city. I’m just really happy just to have this chance.”