Casper Ruud believes Jannik Sinner is not unbeatable but the rest of the field will have to catch the world No 1 on a favourable day as they try to stop him winning a record-extending sixth consecutive Masters 1000 title on home soil at the Italian Open.

“His results this year kind of speak for themselves,” said Ruud. “Four Masters 1000s in a row to begin the year. Four of four. He’s already made history, he can make more history. But he also showed in the beginning of the year, he’s beatable. Novak [Djokovic] beat him. [Jakub] Mensik beat him.

“But when he’s on, not many can touch him. I would say that when both him and Carlos [Alcaraz] are on their highest level, they’re kind of unreachable for the rest at the moment. It’s a reason why they have won the last [nine] slams, these two guys.”

Despite Sinner playing only one match so far, easing past Sebastian Ofner in straight sets in his second-round match on Saturday night, his prospects look even stronger than at the start of the week because of the struggles of many other top players. The first few days in Rome have been disastrous for the highest-ranked challengers, with Djokovic, Félix Auger-Aliassime, Ben Shelton and Alex de Minaur, the players ranked No 3 to No 6, losing in their first matches. On Saturday the 15th seed, Arthur Fils, one of the most in-form players, then retired early in his opening match due to a hip injury. Mensik, the last person to beat Sinner, lost meekly in his second-round match.

Ruud, the 23rd seed, has also struggled recently and this week marks his first outside the top 20 since 2021 as a consequence of not defending his title at the Madrid Open. However, he reached the fourth round on Sunday with an excellent 6-3, 6-4 win over the 11th seed, Jiri Lehecka.

He was succeeded as champion in Madrid by Sinner, whose record-breaking run of Masters 1000 titles has led to some discussions about the possibility of the Italian achieving things that most people had never even considered were possible, such as holding all nine Masters 1000 titles at once. The 24-year-old is now more than halfway there.

Ruud believes it would be impossible for Sinner or any other player to hold all nine Masters 1000 titles, primarily because of how the calendar falls. “After Wimbledon, if you make the finals of Wimbledon, to be ready in Toronto or Montreal is pretty much impossible,” he said. “You just played the final or won the biggest title maybe there is in tennis and then 10 days later, you have to be fit to leave for North America. So I think we’ve seen already a couple of times that whoever does well in Wimbledon, they tend to skip Montreal or Toronto. And I think that will probably continue to happen, unfortunately, for the tournament with the schedule that we have.”

Ruud was joined in the fourth round by Lorenzo Musetti, the eighth seed and Italian No 2, who pulled off an emotional 7-6 (7), 6-4 win over the 25th seed, Francisco Cerúndolo.

Elsewhere, Naomi Osaka continued to build rhythm and momentum as she produced her best win of the year, dismantling the 19th seed, Diana Shnaider, 6-1, 6-2 to reach the fourth round.

There were few problems for the surviving leading seeds, with Jessica Pegula demolishing Rebeka Masarova 6-0, 6-0 and Elena Rybakina rolling past Alexandra Eala 6-4, 6-3. Aryna Sabalenka, the women’s No 1, was knocked out on Saturday by Sorana Cirstea.