“To me, this is overwhelming,” Lucic-Baroni said. “I will never forget this day and these couple of weeks.”
Ranked just 79th, she is one of two unseeded players to reach the Australian Open women’s semifinals this year, joining CoCo Vandeweghe, a 25-year-old who will face Williams on Thursday.
Lucic-Baroni will play Williams’s sister, No. 2 Serena Williams, who beat No. 9 Johanna Konta, 6-2, 6-3, later in the day.
“I’m going to try to stay calm,” Lucic-Baroni said. “I enjoyed every second out here, and I will try to do the same next time.”
She added: “Serena is our greatest champion for sure; the greatest tennis player that ever played the game. So it’s going to be incredibly tough.”
Lucic-Baroni is the third-lowest-ranked woman to reach this stage of the Australian Open. Claudia Porwik of Germany in 1990 and Serena Williams in 2007 were both ranked No. 81 when they made it to the semifinals. Williams went on to win the title.
Justine Henin, the former Belgian star, reached the final in 2010 without a ranking after returning to the game in Australia from an extended break.
Lucic-Baroni arrived this year with a new coach — the Croatian former touring pro Marin Bradaric — and a positive attitude.
“We started working together in November,” Bradaric said after the match, between congratulatory hugs with coaches and players in the corridor next to the players’ restaurant. “She was my idol when I was young.”
He added: “I honestly couldn’t believe she was ranked in the 70s or 80s. For me, she had the talent to be in the 20s.”
Having gained the semifinal, she is now assured to be ranked at least 29 after the tournament.
At 31, Bradaric is three years younger than Lucic-Baroni and was barely in his teens when she began finding success on the women’s circuit. Precocious and poised, she won the 1998 Australian Open women’s doubles titles with Martina Hingis and reached the semifinals of Wimbledon in singles in 1999 by wielding some of the game’s most powerful groundstrokes.
But her elite playing career screeched to a halt because of personal problems, and she did not appear in a Grand Slam singles event for more than seven years from 2003 to 2010.
“One day, I will say a long, big story about all the things that happened to me,” she said Wednesday. “But I never dreamed about being here today.”
Still, she had plenty of chances to get ahead of herself after winning the first set and jumping out to a 2-0 lead in the second by attacking Pliskova’s second serve and dictating play with her forehand.
But Pliskova, who reached the United States Open final last year after beating both Williams sisters, found her range and forced a third set.
It was a big-hitting match full of momentum shifts — Pliskova, 24, and Lucic-Baroni each broke serve seven times — but it did not turn for good until Lucic-Baroni left the court trailing by 3-4 in the final set and took a medical timeout for what she said was treatment on her left leg.
She returned after a break of several minutes and hit sliced aces on the first two points, a first serve and forehand winner on the next and one more sliced ace to hold at love.
She then broke Pliskova at love to go up by 5-4. Before Lucic-Baron came out to serve for the match, she reached into her bag on the changeover and took out a rosary to wear on the court.
“It was really difficult because, like I said, when I took the medical timeout, I wasn’t really sure how I was feeling,” Lucic-Baroni said. “I felt in that moment only God can help me. And yeah, it was just something I didn’t think about.
“It was just something that helped me be strong. I didn’t really plan it.”
On match point at 40-15, Pliskova turned her back and made Lucic-Baroni wait. But what was a delay of a few seconds after an 18-year wait to return to a major semifinal? Lucic-Baroni missed her first serve, but her second found the box, and when Pliskova’s forehand return hit the net, Lucic-Baroni looked over at Bradaric and her support group and made the sign of the cross.
After shaking Pliskova’s hand, Lucic-Baroni stumbled in her team’s direction again and then dropped to her knees, buried her head in her hands and began to cry.
She was not alone.