Rangers were behind early on in the Scottish Premiership clash after Christie Elliott put Dundee in front with just six minutes on the clock.
Gers skipper James Tavernier missed from the penalty spot three minutes before half time as the league’s bottom club went in at the break ahead against the champions.
Van Bronckhorst brought on Fashion Sakala and Joe Aribo at the break and Rangers then levelled through Aaron Ramsey in the 64th minute.
Rangers then scored again in the 86th minute through Connor Goldson to claim a vital three points in the title race and Duffy feels the visitors were a different team in the second half.
He hailed Van Bronckhorst for his tactical changes and said on BBC Sportsound: “Rangers changed everything in the second-half. The mentality, attitude, tempo and personnel.
“Their squad strength was a major factor in turning the game and Dundee just got worn down.
“It was a tactical masterclass from Giovanni Van Bronckhorst”, Duffy added.
Rangers remain three points behind leaders Celtic in the Scottish Premiership table following the win.
