AFL great Mark Williams will have one of the best seats in the house when he joins Jannik Sinner's team in the star's box for the Australian Open men's singles final on Sunday night.

The unlikely pairing has come about thanks to Sinner's Aussie coach Darren Cahill, who has family ties to Williams through the Port Adelaide football club.

Cahill's father John was coached by Williams' father Foster as a player before he went on to take charge of the team himself from 1974 to 1982. 

John Cahill made Williams captain of Port when he left to coach Collingwood in 1983, and Darren revealed the team played a huge role in his success as a mentor to tennis stars like Lleyton Hewitt, Simona Halep - and now, Sinner.

'Ninety five per cent of my coaching throughout my entire career was learnt through the Port Adelaide Football Club,' he told the Herald Sun.

'It's just what I was brought up with, with my dad coaching there for so mamny years and being successful.

'There are some habits and some cultures and some ways of coaching that never leave you.'  

John Cahill coached Port to South Australian National Football League premierships in 1977, 1979 and 1981 after starring in 264 games for the side as a player.

Williams is known for coaching Port Adelaide to their only AFL premiership in 2004 after a distinguished playing career that saw him run out for West Adelaide, Port, Collingwood and Brisbane.

Darren Cahill also opened up on the turning point in Sinner's career ahead of his Open final match against Daniil Medvedev.

Cahill said Sinner's five-set defeat against the Serbian superstar in the Wimbledon quarter-finals 18 months ago was a harsh but necessary lesson for the youngster.

The Italian blew a two-set lead, with Djokovic going on to down Nick Kyrgios in the final and lift the trophy for a seventh time.

'The match he played against Novak at Wimbledon went a long way to teaching Jannik where he needed to get better,' said Cahill.

'When he was up two sets to love and lost that five-set match against Novak, you're able to sit down with him and talk about where the improvements needed to be made.

'And credit to him, he absorbed it.

'He gets on the practice court, he takes the information and he loves to work on things that are going to make him a better tennis player.'

Cahill joined Sinner's camp through that grass campaign and takes a share of the credit for the player's subsequent rise up the rankings.

Working alongside co-coach Simone Vagnozzi, Cahill has helped improve Sinner's game smarts, fitness, serve, and self-belief.

Cahill said two victories within a week last November over Djokovic, as well as steering Italy to their first Davis Cup title since 1976, had fuelled the youngster's confidence.