The Williams sisters, Venus and Serena, once owned tennis as if it were a private business. On Saturday they will resume the partnership in the final of the 2017 Australian Open after victories on Thursday that were oceans apart in style and content, but which began in the same boat more than three decades ago.

At 36, Venus, the elder Williams sister who still has to battle through occasional bouts of the Sjogrens Syndrome that struck her down six years ago, nevertheless showed over nearly two-and-a-half hours on another hot day on Rod Laver Arena that she was healthy and good enough to beat Coco Vandeweghe in three sets to reach Saturday’s final of the Australian Open for the first time in 14 years.

Venus Williams beats CoCo Vandeweghe in Australian Open semi-final – as it happened Read more

As she said so eloquently on court after coming from a set down against a compatriot 11 years her junior to win 6-7 (3-7), 6-2, 6-3, “Everyone has their moment in the sun. I’d like to keep it going. I’ve got nothing else to do.”

The warmth of the crowd’s reception when she leapt around in a victory dance that seemed it might never end gave her sense of self-worth a boost it probably has needed for a very long time. Playing through illness and in the shadow of her sister, Serena – whom she will play in the final – is a double-weight that would crush a lesser player.

Serena, a year young than Venus and three-times as garlanded with 22 majors, beat Mirjana Lucic-Baroni – a mere 34 years old – with ominous ease in the second semi-final, 6-2, 6-1, in 50 minutes. There could hardly be more contrasting wins – and there will be some who wonder again about the symbiosis between them: how hard will Serena strive to pass Steffi Graf’s Open era number of majors, when she knows what an eighth slam title would mean to her sister?

Subconsciously, there must be a conflict – one she hinted at in a television interview with Andy Murray’s former coach Brad Gilbert afterwards. “Obviously I want to go out and play well, but I always root for her,” she said.

It is the comeback of Venus that was the biggest of several talking points in this draw. Her last final here was 14 years ago. Her most recent slam final arrived in 2009 at Wimbledon, when she lost to Serena. They reached these semi-finals – the 12th time they have done so in the same slam – without dropping a set but Venus did well to recover from a set down, when she was under serious pressure.

“Oh my god, it means so much, mostly because Coco played so well, so unbelievable. I had to play defence the whole time. There was never a moment of relaxation, ever.”

She added: “To get to the final, it means so much. It’s more than the cherry on top, more than I dreamed of. I have to give her credit on match point, she just kept swinging. I don’t even remember what happened.”

Speaking before her sister’s match, she said: “It’s an unbelievable thing to watch Serena Williams play tennis. I would more than anything like to see her across the net from me on Saturday.”

There have been more fairytales at this tournament than in the collected works of Hans Christian Andersen. The average age of the semi-finalists, three of them Americans, was 32 years and six months, the oldest of any quartet to get this far in the Open era.

Facebook Twitter Pinterest Serena Williams celebrates reaching the Australian Open final. Photograph: Tracey Nearmy/EPA

Lucic-Baroni – who played Serena twice before, both matches in 1998 – will jump 50 places to a career-high 29 in the world at the age of 34, after beating two top five players to reach the semi-finals. Only three players have gone this deep in a slam with ranking lower than 79. Her back story, too, is one of hardship and struggle, escaping the oppressive regime of her father, enduring injury after a promising start and running into financial problems before returning to the game that still means so much to her. Hers, like that of the others, is a story for the ages in every way.

“She’s an inspiration,” Serena said. “She really deserves all the credit today. To get this far after all she’s been through, really inspires me. I’ve been watching her whole tournament, rooting for her the whole time.”

As for Serena’s game, it hit another pitch of excellence on Thursday, whatever the self-deprecatory opinion afterwards. “The serve was a little better today, but I’m getting there,” she said. “I knew I had to serve well, and take my chances as early as I could.” That was taking understatement to a ridiculous level. She lost just two points on her first serve, 10 in all, but only had time to hit three aces, bringing her total from six matches to 44, one behind the player her sister beat.

So “zoned” was Serena before stepping on court, she did not pay attention to the first semi-final, and, when the sisters crossed in the tunnel, they did not stop for pleasantries. This was business.

“I didn’t watch the match before but I was really proud of Venus, total inspiration, big sister. She’s my world and my life. She means everything to me. For us both to be in the final is the biggest dream come true for us. She’s my toughest opponent. Nobody has beaten me has much as Venus. Whatever happens we’ve won. She’s been through a lot. I’ve been through a lot. A Williams is going to win this tournament.”

Nor was she bothered about playing on consecutive days, backing up her quarter-final on Wednesday with Thursday’s win. “You have to get better as a tournament goes on. For me, back-to-back is fine. In fact, I was so bored, because I wasn’t playing doubles. Going for walks.”

Will Saturday be another walk in the park? For the good of the game, we all ought to hope not. Venus is, indeed, Serena’s toughest opponent. If she were to do the improbable and beat her again, it would be her 12th sibling triumph in 26 attempts. Not bad.