(Photo credit: Aaron Doster-Imagn Images)

Second-seeded Carlos Alcaraz won the Cincinnati Open title on Monday when top-seeded Jannik Sinner retired due to illness in the first set in Mason, Ohio.

Sinner labored from the start in the intense heat and Alcaraz took advantage and took a 5-0 before a highly emotional Sinner called it a day after 23 minutes.

Alcaraz won 21 of the 29 points and Sinner committed a whopping nine unforced errors before he retired.

'I'm really sorry to have to pull out today,' Sinner told the crowd during the trophy ceremony. 'I'm super, super sorry to disappoint you.'

Sinner, who turned 24 on Saturday, said he started to feel ill Sunday and hoped his health would improve overnight. Instead, the Italian star said he felt worse.

'I tried to come out and tried to make it at least a small match but I couldn't handle more so I'm very, very sorry for all of you,' Sinner said. 'I know that maybe some of you on Monday had to work or had to do something else so I'm really, really sorry.'

Alcaraz improved to 9-5 against Sinner in his career and a dominant 8-1 in all ATP 1000-level finals, but he would have preferred having a slugfest Monday as opposed to the short time on court. The 22-year-old from Spain is the youngest men's champion of the Cincinnati Open since Britain's Andy Murray (age 21) in 2008.

'This is not the way I want to win this trophy,' Alcaraz said, before looking at Sinner. 'I've told you many times you are a truly great champion. I'm pretty sure you will come back better and even stronger, you always do.'

Sinner and Alcaraz will again be favorites to reach the final of the U.S. Open, which starts Sunday in New York.

Alcaraz has won five titles in his last seven events, including a classic five-set win over Sinner to take the French Open crown. Sinner was 31-3 this year before Monday and won two major titles -- the Australian Open and Wimbledon.

'It was a great tournament for me,' Alcaraz told the crowd. '... Thank you for the week and I'm blessed I was part of the tournament this year.'

Sinner was the defending Cincinnati Open champion.

--Field Level Media