Cantwell has made an impressive return since missing Rovers’ opening match and will hope for more of the same against his former club Norwich next Saturday, when Hull will look to bounce back away to Bristol City.
Hedges, who had not scored since last August, put Blackburn ahead with a classy finish on 18 minutes.
Sidnei Tavares headed towards Augustus Kargbo and the Sierra Leonean’s clever pass set up Hedges, who coolly dinked the ball over keeper Ivor Pandur.
The goal came against the run of play – and after Blackburn keeper Balázs Tóth had produced three key saves in the space of a couple of minutes.
Tóth prevented a Yuri Ribeiro own goal and, from the resulting corner, kept out Oli McBurnie’s header, before quickly being called into action again, this time to save Joel Ndala’s effort from near the edge of the penalty area.
The visitors continued to have the upper hand after going ahead, with Hedges heading Ryan Alebiosu’s cross over and Karbo firing wide.
And two Rovers goals in the space of three minutes early in the second half crushed any real prospect of a Hull comeback.
First, the Tigers defence was caught out by Cantwell’s clever free-kick, played to the left-hand side of the penalty area to Hedges, whose ball in towards Ohashi bounced off the Japanese striker and into the net.
Then Alebiosu bundled his way past a feeble challenge from Ryan Giles on the right and sent in a cross which was parried by Pandur straight to Cantwell, who helped himself to his second league goal in as many appearances.
There was almost a fourth soon afterwards as Dominic Hyam launched himself at Cantwell’s left-wing corner and the ball struck the defender’s back and then the crossbar.
Hull rarely threatened – and looked vulnerable on the counter-attack, with Pandur denying Ohashi and Hedges failing to apply the finish when he seemed certain to score.