A fourth-round collision on Monday that will rip the 2019 Australian Open wide apart brings the official world No 1, Simona Halep, and the best player in the history of the game, Serena Williams, together for the ninth time.

The American has an 8-1 grip on that rivalry, but the Romanian comes into the match after beating her sister, Venus, fairly convincingly on day six, 6-2, 6-3 in a little more than an hour-and-a-quarter. However, the younger Williams sister has been in equally awesome form in the first week, taking just over an hour to beat the Ukrainian teenager Dayana Yastremska for the loss of just three games.

There was a touching moment at the net, when Williams comforted Yastremska, who could not hold back the tears. “I could tell she was quite upset,” said Williams. “I kind of liked that. It shows she wasn’t just there to play a good match, she was there to win. She wanted to win. That really broke my heart. I think she’s a good talent. It’s good to see that attitude. I remember one time in particular against Venus at Wimbledon, as I was walking to the net, I started bawling. I couldn’t help it.”

It will be back to business against Halep, though, and a step up in levels. The Romanian, lifted after breaking through at Roland Garros last summer after years of near-misses in the majors, dropped a tie-break set in the first round against Kaia Kanepi, and another when beating the American Sofia Kenin. But she found the right gears against Venus.

“She played pretty flawless tennis today – only 12 errors,” Williams said. “Unfortunately, I had almost three times as many.”

So a match worthy of a final awaits. Also on that side of the draw is Serena’s conqueror in the US Open final, Naomi Osaka, who had to come from a set and 2-4 down to get past the quirky genius of Hsieh Su-wei. Madison Keys is also through and in good enough touch to beat the sixth seed, Elina Svitolina, who needed three sets to beat the unseeded Shuai Zhang in two hours and 55 minutes, the longest match in the women’s championship so far.

Serena Williams serves against Dayana Yastremska. Photograph: Mast Irham/EPA

For all that, Serena Williams seems scarily focused in pursuit of one more major to move alongside the all-time record of Margaret Court. In that mood, she can be unbeatable.

The former British No 1 Annabel Croft, working here for Eurosport, said of Williams: “She looks a lot more at ease with the situation, this looming 24th grand slam – which has rather shackled her in the finals of the last two grand slams. I get the feeling she is come to terms with it and is ready to play freely, enjoy the situation and take on the challenge.”