Celtic’s 3-0 win over Rangers at home on Wednesday night took them to the top of the Scottish Premiership table, one point clear of their Glasgow rivals.
Rangers won the league title by 18 points last season and were favourites to win the league this term as well but Celtic have gradually built towards getting back to the top under Postecoglou.
The Australian’s appointment was doubted by many last summer and his affinity to recruit from Japan also came under the scanner.
But Duffy feels that the Celtic boss has come through all that and has proven the doubters wrong through his side’s performances.
He also lauded Postecoglou for sticking to his principles and beliefs despite the initial criticism.
Duffy said on Clyde 1’s Superscoreboard: “You can’t underestimate the job he has done.
“He came into the country, the people were saying what do you know about Scottish people, then he signed the Japanese players and then, ‘he shouldn’t be bringing players from Japan, they wouldn’t adapt to Scottish football and the intensity and the physicality’.
“He has proven everybody wrong time and again and he has single-mindedness, and I think you need that at a big club like Celtic.
“You can’t listen to too many opinions, you have got to go in there with your beliefs, your philosophy and stick to it.
“And that’s what he has done.”
Rangers are snapping at their heels still but Celtic are now in a strong position to wrestle back the title this season.
