David Bentley enhanced his England credentials with a brilliant 66th-minute strike to help steer Blackburn into the Carling Cup fourth round.

The 23-year-old, who was widely jeered when he made his senior international debut against Israel earlier this month, produced a delightful effort from 25 yards which flew into the top corner.

Matt Derbyshire added the second from the penalty spot 10 minutes later and substitute Roque Santa Cruz netted a late header to finally end the spirited resistance of an effectively reserve Birmingham side.

Earlier, Birmingham goalkeeper Richard Kingson sustained a sickening injury as the third-round tie was held up for seven minutes.

The Ghana international smashed his face against a post in the 40th minute when contesting a David Bentley free-kick with Rovers defender Chris Samba.

Kingson, 29, required several minutes of treatment by medical staff but was eventually stretchered off and replaced by Colin Doyle after producing a string of fine saves prior to his injury.

In the second minute, David Bentley whipped a delightful curling free-kick into the outside of the side-netting from 20 yards before delivering a pinpoint corner onto the head of Derbyshire.

The England Under-21 striker made decent contact but his effort was blocked and Birmingham breathed again.

Blackburn continued to build momentum and another Bentley cross from the right again found Derbyshire lurking in the six-yard box.

He connected and looked to have done enough to beat Kingson, but Stuart Parnaby showed outstanding alertness to nod the ball off the line to prevent a certain goal.

David Dunn, who rejoined his hometown club in January after three-and-a-half injury-plagued years at Birmingham, then showed his old boss Bruce what he really is capable of.

Some nimble footwork allowed Dunn to engineer the space for a shooting chance 20 yards from goal in the 25th minute, but Kingson did well to beat his low effort away.

Blackburn sought to raise the tempo after the break but Dunn's furious calls for a handball from his shot amounted to nothing.

Six minutes after the break Dunn slipped Roberts clear and the striker capitalised on Radhi Jaidi's slip to race through on goal.

He had only Doyle to beat but fired horribly wide before collapsing in a heap, apparently injured, before being replaced by Roque Santa Cruz.

His arrival gave Blackburn fresh impetus and after surviving a scare when Mokoena blocked Garry O'Connor's shot in the 53rd minute, Bentley struck 12 minutes later.

Collecting possession 30 yards from goal, he glided effortlessly past Damien Johnson and struck a brilliant diagonal right-foot shot which flew past Doyle and nestled in the top corner.

Roberts had only Doyle to beat but fired horribly wide before collapsing in a heap, apparently injured, before being replaced by Roque Santa Cruz.

His arrival gave Blackburn fresh impetus and after surviving a scare when Mokoena blocked Garry O'Connor's shot in the 53rd minute, Bentley struck 12 minutes later.

Derbyshire claimed the second with 10 minutes remaining when substitute Rafael Schmitz fouled him and Santa Cruz applied the coup de grace with a late header from Brett Emerton's cross.