WATCH the Cincinnati Open LIVE in Australia on beIN SPORTS | Subscribe here and take advantage of our 7-day FREE TRIAL

The defending champion had lost both of their encounters, winning just one set. However, those defeats came  in 2022, before Sinner cracked the Top 10 in the ATP Rankings. Now the World No. 1, the Italian showcased just how far he’s come, dictating terms on center court to earn a dominant 6-0 6-2 victory.

"I felt that I was returning very well today," said Sinner, who won 80 percent of points on Auger-Aliassime's second serve. "I think that was the key point, which gave me the confidence to serve well. I had a small drop in the second set when he broke me. It could have been a small change but I am happy I broke him back quite early.

"He is a very difficult opponent because he serves well, he moves well. Physically in incredible shape and hits the forehand very well. But we prepared in the best way, also tactically and I felt like today I was playing some great tennis."

Sinner, who has yet to drop a set in Cincinnati, claimed his quickest win of 2025 in his opening-round triumph in Ohio, defeating Daniel Elahi Galan in just 59 minutes. By moving past Auger-Aliassime in 71 minutes, the Italian came close to matching that time.

Auger-Aliassime struggled to hang with Sinner in the opening set, committing 13 unforced errors. The 23rd seed did lead 2-0 at the start of the second but quickly faded. He struck eight double faults and could not find his rhythm from the baseline, with the 23-year-old too consistent to storm to victory. He will next play Holger Rune or Terence Atmane.

"Today I felt great on court," Sinner added. "I think you saw that but every day is going to be different. Tomorrow is a day off, which is good for me. We will try and put some reps in and then see what I can do in the semis."

With his triumph, Sinner extended his winning streak on hard courts to 25 matches. The Italian is just the fifth man this century to record 25 consecutive victories on the surface alongside Roger Federer, Novak Djokovic, Rafael Nadal Andy Murray. The Italian’s last defeat on hard courts came against Carlos Alcaraz in the Beijing final in October, with Sinner winning titles at the ATP Finals and the Australian Open in the past year.

Playing his first tournament since winning his first Wimbledon crown, Sinner is 30-3 on the season. Just seven wins away from 300 career victories, Sinner earlier in the month became the second player to qualify for November's ATP Finals, joining Alcaraz.

Sinner and Alcaraz will compete in a thrilling battle for ATP Year-End No. 1 honours over the remaining months of the year. Alcaraz holds a 1,440-point lead over Sinner in the ATP Live Race To Turin and is in Cincinnati quarter-final action against Andrey Rublev.