The Italian departed after just 13 games at the helm in September last year, with morale at the club shattered following a disastrous start to the season.
By the time Gus Poyet replaced him, the Black Cats had collected just a single point from their opening seven Barclays Premier League games, and although it has been far from plain sailing since, the Uruguayan has sparked a significant recovery.
Sunderland will entertain Southampton on Saturday having dragged themselves off the foot of the table and to within a point of safety, although what has happened behind the scenes has been just as important.
Bardsley told the Sunderland Echo: "You have got to have a very good team spirit. I think that was beyond dead six months ago. Now we have dug it out.
"The manager came in and gave the players a new lease of life, and everyone is taking their opportunity. That's what you need week in, week out because there's decent competition at the club.
"When I came in, the team only had one point, but now we are on the way to getting out of it."
Four days after the home clash with the Saints, the Black Cats will head for Manchester United defending a 2-1 Capital One Cup semi-final, first leg lead, but it is the fight for top-flight survival which remains the priority.
That looked a long shot just a few weeks ago, but a run of six league games which has brought just one defeat and, more importantly, two victories, has rekindled belief.
Bardsley said: "Absolutely, we believe we can do it. We are in our own mini-league and if we win on Saturday against Southampton, we are three points behind Hull in 10th.
"That's unbelievable when you look back three or four weeks ago. We need to just focus on ourselves and win as many games as possible."
On a personal note, Bardsley continues to thrive after appearing to be on his way out of the club following the breakdown of his relationship with Di Canio.
The 28-year-old full-back was sent to train with the club's Under-21s during the summer, but since being recalled to the fold by Poyet he has made himself all but indispensable.
Bardsley said: "It was probably one of the lowest points of my career, to be honest with you. But when the manager called me back into the squad, I knew I had more to offer this football club.
"I'm thankful for the opportunity he gave me and I thought I had to repay him with performances. Hopefully I'm doing that."