Zverev seeks US Open last eight as Osaka faces Rybakina

Top-seeded Alexander Zverev headlines the action at the US Open on Monday, taking on Luciano Darderi for a place in the quarter-finals.

After two marathon five-setters to open his campaign, French Open champion Zverev had a smoother ride against Alejandro Tabilo and he'll be looking to improve further against the 21st-seeded Italian.

As he has in each of his matches, Zverev will again anchor the night session on Arthur Ashe Stadium, on a day offering plenty of compelling fourth-round contests.

AFP Sport looks at three matches to watch on Day 9 of the US Open:

Rybakina leads head to head 1-0

-- World number two Elena Rybakina has brushed off talk of the No. 1 ranking, but the pressure is nevertheless on the two-time Grand Slam winner from Kazakhstan, who only needs to reach the semi-finals to knock Aryna Sabalenka out of the top spot.

The reigning Australian Open champion has yet to drop a set, but she'll be stepping up in class against Osaka -- whose four Grand Slam titles include two US Opens.

More than two years since she returned to the tour after an extended maternity leave, Osaka is on an upward trajectory.

She reached the Australian Open third round, made the last 16 at Roland Garros and had a best-ever quarter-final run at Wimbledon that included a victory over Sabalenka.

She'll have to avoid the mid-match dips that marred her victories over Katerina Siniakova and Elise Mertens if she's to have a chance to knock off Rybakina.

"I know she's one of the best players in the world, so I have no choice but to come with a high level," Osaka said. "I think that's when the most exciting tennis is."

Blockx leads head to head 1-0

-- Upset third-round victories propelled Cerundolo and Blockx into new US Open territory.

Cerundolo, the highest-ranked Latin American player on the ATP Tour, rallied from two sets down to topple ninth-seeded American Taylor Fritz and continue his best-ever run in Flushing Meadows.

The 21-year-old Belgian Blockx, seeded at a major for the first time, shocked fifth-seeded French Open finalist Flavio Cobolli in four sets to reach the second week of a Grand Slam for the first time.

Ranked 116th in the world 12 months ago, Blockx said that was his goal coming in -- one he'll now need to re-set.

That starts with Cerundolo, who fell to Blockx in their only prior meeting at the clay court Madrid Masters this year.

"Now, conditions are completely different," Blockx said. "We are both really confident, playing good tennis, so it will be an exciting match."

Swiatek leads head to head 7-1

-- Six-time Grand Slam champion Swiatek may have the upper hand in this rivalry, but Zheng's lone win over the Polish star was a big one -- in the semi-finals of the Paris Olympics on the way to singles gold.

Since that triumph, Zheng has seen her rise derailed by injury, with a lengthier than expected return from elbow surgery last year seeing the former world number four's ranking plummet so far that she had to come through qualifying to gain a US Open berth.

She'll ride the momentum of an epic comeback into her fourth-round clash with Swiatek, having rallied from 0-5 down in the final set to stun Madison Keys in three in the third round.

The last qualifier to reach the US Open women's singles fourth round was Emma Raducanu -- who went on to win the title in 2021.

Swiatek will be a big obstacle in Zheng's path to a similar feat. Although she has endured a disappointing year by her standards, the Pole has come on strong in the build-up to the Open, capturing her first title of the year in Toronto.