W2W4 at Australian Open: Andrey Rublev, Marta Kostyuk poised to pull off upsets

With two full rounds complete, our latest bracketology reports morph from wild guesswork into something approaching science. What they tell us about the Australian Open right now is that the third quarter of the WTA draw, in which all the top seeds but No. 4 Elina Svitolina are gone, is up for grabs.

On the men's side, a number of big names from the top quarter of the draw will face significant third-round tests, though top-seed Rafael Nadal probably isn't one of them. He gets No. 28 seed Damir Dzumhur. Some of the other marquee names in that quarter face competition that, on paper, is much stiffer.

Let's look at three of the most compelling Day 5 matchups:

No. 3 seed Grigor Dimitrov vs. No. 30 seed Andrey Rublev (Rublev leads series 1-0)

Dimitrov, once saddled with the nickname "Baby Fed" and long expected to live up to it, is 26 years old, ranked No. 3 and clicking like castanets with his coach, Dani Vallverdu. Why should he be worried about a 20-year-old Russian who stands 6-foot-2 but barely weighs 150 pounds?

Because Rublev, second only to No. 4 Alexander Zverev in the under-21 ATP rankings, knocked Dimitrov out of the US Open in August in the second round. Rublev also appears to have the drive, consistency and maturity that Dimitrov lacked at a comparable age. Finally, Dimitrov barely survived his last match against a guy playing in his first main draw at a major.

Rublev has been rising steadily, almost implacably. He started last year ranked No. 152 but won his first ATP event (Umag) by mid-July. A punishing baseliner with a monstrous forehand, Rublev will probably try to hit through his more versatile, fluid opponent. If Dimitrov is at all leg weary, he might find himself in trouble.

No. 4 seed Elina Svitolina vs. No. 521 Marta Kostyuk (first meeting)

Something special is happening Down Under. Kostyuk, a 15-year-old qualifier, is breaking out. She has won two main-draw matches and is already being hailed as the Next Great Thing in women's tennis. This upcoming match isn't going to be about Svitolina at all, despite her high seeding and status as last year's winningest WTA player (five titles). That's a problem, but not for Kostyuk.

Strange things happen to veterans when extraordinary, young prodigies come along. They have trouble handling the situation. It's a particularly hazardous moment for Svitolina because despite her general consistency, she has always struggled to play up to snuff at majors. She has won 10 titles and has been ranked as high as No. 3. But she has advanced to the quarterfinals at just one major, the French Open.

Both women are Ukrainian, but don't expect Kostyuk to be deferential or intimidated. She might be a chatty Cathy, but she's shrewd and well aware of the advantage her age provides. As Kostyuk told the media following her last win: "I think I'm going to play on big court again, but I will just try to show my best tennis. I'm pretty sure [that] like all my opponents, she will struggle a little bit, and I will try to use this."

Svitolina is a bread-and-butter baseliner. She has nothing in her repertoire that Kostyuk hasn't seen a million times, despite her tender age. Unless Kostyuk's exploits thus far leave her drained, the match will come down to consistency -- and nerves.

No. 15 Jo-Wilfried Tsonga vs. No. 17 Nick Kyrgios (Tsonga leads 1-0)

This much is sure: This match will produce some spectacular shot-making. At 32, the window is quickly closing on Tsonga's chances to win a Grand Slam -- an achievement that seemed a certainty when he made the finals of this tournament in 2008. That was a decade ago, when Tsonga was exactly the age Kyrgios is now. It ought to give Kyrgios a lot to think about.

Tsonga's ranking slipped in the past 12 months, partly because of injuries and the birth of his son. He managed to win a career-best four titles on the year, on three different surfaces. It would be a mistake to underestimate him.

Kyrgios is once again speaking as if he has turned a new leaf and is ready to fully realize his talent. This match will be a great test of his resolve as well as his progress because Tsonga is playing well and won't be pushed around. The muscular 6-foot-2 Frenchman is likely to make this a tough, highly physical match, hammering down big serves and pulling whippet-lean Kyrgios all over the court to execute passing shots. It will probably take patience and stamina, things Kyrgios doesn't always have in abundance, to win this one.

Upset special

It's tempting to pick Andrey Rublev over Dimitrov, but let's go with the hype and predict a win for young Marta Kostyuk over Svitolina, who fails to elevate her game adequately at majors.