Until as recently as two years ago, one of the defining moments of Caroline Wozniacki’s career was the one she spent years trying to forget. Wozniacki was ranked No 1 when she stared down Li Na in the semi-final of the Australian Open in 2011 and it had all the makings of a typical Wozniacki win: she chased down every last ball and gave nothing away, flitting to within a point of her second grand slam final at 20 years old.

On match point Wozniacki changed nothing, but across the net adrenaline coursed through Li’s veins as she made her last stand. She stepped inside the court and seized the moment, bulldozing a down‑the-line forehand winner to scupper her opponent before turning the match around in three sets.

The defeat was so devastating for Wozniacki that, when she returned to the semi-final seven years later, it was still on her mind. “I had match points against Li Na,” she said in 2018. “I lost it. That’s still haunting me to this day.”

The loss would change the discourse around Wozniacki from bright new star to a player with fundamental flaws in her game and an asterisk beside her ranking. Wozniacki is one of the most defensive players to reach No 1 – she even ushered in the return of the moonball – and overly defensive players are often sneered at. Although Wozniacki consistently ground down top opponents in regular tournaments, deep in the biggest events the best shot-makers would rise to the occasion and hit her off the court.

Wozniacki finished 2010 and 2011 ranked No 1 with 12 titles in two years, but her inability to complement those results with a slam helped to embed a new pejorative in the tennis lexicon: “Slamless No 1.” People questioned why her serve could scale 118mph but her forehand could not crack open an egg. Fingers often pointed directly at her father and coach, Piotr.

On Friday, Wozniacki announced that she will retire after the Australian Open in January. “I’ve always told myself, when the time comes, that there are things away from tennis that I want to do more, then it’s time to be done. In recent months, I’ve realised that there is a lot more in life that I’d like to accomplish off the court,” she wrote on social media.

Although Wozniacki is 29 in a world where the 38-year-olds Roger Federer and Serena Williams are still going strong, this is no surprise. Last year, she was diagnosed with rheumatoid arthritis and competing with it this year has been tough. Her ranking has fallen to 38th after returning to the No 1 spot last season.

Her diminished stamina and chronic stiffness directly affect her physical strengths and it has left her body more brittle. Off the court, Wozniacki married her fiance, the former NBA player David Lee, and as she took her first extended glance towards her future, she looked back at her sport with a changed perspective. Wozniacki always said that she did not plan on competing deep into her thirties. This was an opportunity to depart joyfully on her terms and she took it.

Caroline Wozniacki celebrates her first grand slam title after beating Simona Halep at the 2018 Australian Open. Photograph: Edgar Su/Reuters

Wozniacki’s beginnings reflect her drive and mental fortitude. Her parents immigrated to Denmark from Poland in the late 1980s, a few years before she was born. There was no solid structure to help her reach the top and the country simply did not produce players until she came along. Wozniacki has frequently played alongside unranked novices in the Fed Cup team.

Since neither Piotr or her mother, Anna, spoke English, from as young as 11 Wozniacki controlled much of her own destiny. She took important telephone calls, translated contracts and liaised with tournament directors, all with the aim of becoming the best in the world.

After their daily practice sessions, Wozniacki and her father would regularly drive around Denmark to pitch her potential to sponsors. They had to convince organisations that a girl from an immigrant background would somehow make it to the top in a country with no top players and then that they should give money to her. Throughout her youth, they were burned by the constant criticisms of her father’s hands-on approach to her career.

Despite the clear obstacles, Wozniacki’s rise proved to be seamless. She became the junior world No 1 and Wimbledon girls’ champion in 2006. As she racked up titles and marched deep into most other tournaments, it always seemed like a slam draw would eventually break apart for her.

Instead, her career after 2012 would be a turbulent cycle of injuries, burnout and comebacks. Wozniacki was a struggling nonentity for nearly two years until she returned unexpectedly in the summer of 2014, storming into the US Open final and eventually returning to the top 10 in a season punctuated by a 3hr 26min 33sec debut New York marathon time after a 10-month tennis season. However, the marathon effort only seemed to invite more injuries; by 2016, Wozniacki had fallen as low as 74th.

Seven years after her loss to Li, Wozniacki stared down two match points at 1-5 and 40-15 in the second round of the 2018 Australian Open against the unheralded Jana Fett. She recovered before outlasting Simona Halep in a grimy, exhausting three‑set match to win her first slam title in oppressive humidity.

Although Wozniacki has made small adjustments to her game over the years, she worked a tired Halep so thoroughly that the Romanian finished the night dehydrated in hospital. The manner of the victory was a reminder that Wozniacki had spent years hearing people tell her she was too defensive and needed a new coach. Although she responded calmly to every question about her limp forehand and overbearing father, she never let those outside opinions sway her into overhauling her game.

Wozniacki’s composure rarely breaks unless she is petulantly battling umpires or verbally jousting with her nemesis, Maria Sharapova, but as she finally achieved the elusive slam that had weighed so heavily on her shoulders, she stared at her father and sobbed in disbelief.

What a triumph to have finally succeeded on her own path and in her own time and likewise to depart from her sport with her head held high and the rest of her life still to come.