When Ajla Tomljanovic was a little girl, she asked her father about a prized photograph of him holding a big trophy on his head. Ratko Tomljanovic was a great professional handball player, winning two European Championships for Zagreb, the capital of Croatia, and was the captain of the Croatian national team; before that, he was a member of the Yugoslavian team.

His daughter wanted to know where that shiny trophy was, because she had never seen it in their home. Ratko Tomljanovic explained that it had been a team award, and that he did not get to keep it. Unimpressed, Ajla told him that she would not play handball. “I want the trophy just for myself,” she said. So Ajla Tomljanovic chose tennis, and she is still striving for that big trophy, for a professional championship. She has shown the talent for it, though her nerves have betrayed her at times — what she calls “the bad Ajla.”

But on Friday night, Tomljanovic, who is ranked 46th, demonstrated to herself and the world that she had the mettle and the shotmaking ability to win a trophy of her own. If she wins four more matches in the coming week, it will be one of the most coveted in sports. That night, Tomljanovic beat the six-time US Open champion Serena Williams, 7-5, 6-7 (4), 6-1. But ahead of the match Tomljanovic was nervous and confided the anxiety to her father. He brought out a motivational tool. He mentioned one of his favourite movies, For Love of the Game, in which a pitcher for the Detroit Tigers, played by Kevin Costner, reflects on his life and career in the midst of a perfect game.

“But she didn’t know the movie, so I had to explain it to her,” he said. “I told her, ‘You have to be Kevin Costner today.’” In the film, he told her, the pitcher focuses explicitly on the catcher’s glove and ignores everything else in the stadium. Ajla understood, and she followed the advice with her own unique resolve. “From the first moment I walked on court, I was in my own little bubble,” she said. After Ajla won, Ratko sat quietly in the player garden. He again saw a little of Kevin Costner.