Tennis is an outdoor pastime involving sweaty folk who strive to hit a ball over a net. It entertains but does not save lives, it amuses but scarcely contributes to world peace, it distracts but does not greatly improve our IQ. But sometimes tennis can play a role in repairing a person.

It was on a tennis court yesterday that Mirjana Lucic-Baroni cried when she won her quarter-final at the Australian Open. Thanked God and knelt and cried. Got up and cried. Hugged the on-court interviewer and cried. Cried maybe for what she had gone through, what she has lost, and what she has finally found. Cried behind those dark glasses till others cried, too.

"To me, this is overwhelming," she said after defeating Karolina Pliskova 6-4, 3-6, 6-4. "I will never, ever, ever forget this day and this last couple of weeks. This has truly made my life and everything bad that happened, (it) has made it OK."

No one knows precisely what Lucic-Baroni, now world No.79, went through and why she left tennis but the crying told us that it had hurt. In 1999, the year Serena Williams won the US Open, Lucic-Baroni was in the Wimbledon semi-finals. A great future loomed, a great absence followed. From 2001 to 2010, she was absent from the main draw of 35 Grand Slam events. To see a chart of her career is to see a gash through it. It was the flight of youth.

There is talk of an abusive father and financial difficulty but no real details. She said the other day: "People think they know a lot about my history, but they really do not. One day when I feel like talking about it, I will. Right now is not that day."

Right now she is playing. Right now if you walk the hallways of the Open you will find her and a gang of tennis pensioners who are demonstrating that class means longevity.

Last night Rafael Nadal said: "I am not an arrogant person so I always have doubts. And when you have doubts you feel ready to work more." It is this work ethic that puts him, 30, Roger Federer, 35, and Stan Wawrinka, 31, in the men's semis. It is this love for a game, for history, for picking a scrap, that has Serena, 35, Venus 36, and Lucic-Baroni, 34, in the ladies' semis.

Once tennis had Wimbledon winners who barely shaved, like Boris Becker, 17, and girls who were No.1 at an age - Martina Hingis at 16 - when they required chaperones. Now, in a lovely coincidence, tennis' greying guard has congregated to confirm that the game has outgrown its romance with teenagers.

Almost everyone in the semis has wrestled insecurity, fought injury, braved a disease or battled breaks from the game. Almost everyone is a testament to will, science and the lure of greatness.

Crowds flock to them, for it is like old friends renewing an acquaintance. These players aren't perfect but they represent hope, they're not some empty, hair-gelled brand but a real story of grit and substance. Of all of them, Lucic-Baroni may have the least distinguished record but she owns the most painful tale. If we are astonished at Federer's return after six months out, then she once went more than six straight years without playing a Slam.

What does it do to the spirit, the confidence, the legs, the technique? Every year you sit out, you age; every Slam you miss, a new player comes. The game forgets you and you forget your playing self.

Belief arrives from winning but she was barely playing. And so belief "was a bit broken for a few years. When I was younger, I just believed because I won a lot and it was that confidence you have because you're winning all the time.

"When you stop winning as much and you don't play for a long time, yeah, you definitely lose it a little bit. Not even lose it, you forget it. You forget deep down kind of who you are on the court."

But then she remembered. She remembered because she fought. She fought because she loved tennis. "You keep pushing and you keep pushing and nothing is working and you keep pushing. That belief that eventually it will change... I think that's what perseverance is and I feel like that's what helped me."

Now she is married and happy and has an easy laugh, but of course she plays. The court is the only place she could complete her story. The court is where she finds a type of feeling "you cannot replicate anywhere else in life". The court - especially the big courts - is where she will feel all that she thought she was destined for but then had to forfeit; the warmth of a crowd and the glow of achievement.

There isn't always a way back in life and sport isn't always the land of fairy tale endings. But to defeat seeds No. 3 and No. 5 and return to a Grand Slam semi-final 18 years after the first one is to tell yourself the simplest and most profound of things: Yes, I can play.

Today she faces Serena Williams, whom she called "the greatest champion" but perhaps she is herself the greatest survivor. So often we hear stories of redemption in sport, but this was even finer. Like a faded painting brought to lovely life, this was an athlete restored.