Reading deservedly led at half-time, midfielder James Harper stroking them ahead four minutes before the break after Steve Sidwell had earlier headed against the crossbar.
But Mark Hughes abandoned a five-man midfield to go 4-4-2 and was rewarded with a dominant second-half display.
It had looked as though it was not going to be Rovers' day as striker Benni McCarthy saw a hat-trick of efforts all ruled out for offside.
But the South African striker headed the equaliser from a Lucas Neill cross and Rovers completed their comeback when Bentley won the ball on the halfway line and burst forward to unleash a sensational long-range strike.
Reading threatened first, Kevin Doyle allowed a 10th minute sighter as he outmuscled Andre Ooijer to reach a Seol flick-on first, only to blaze his left-foot shot well off target.
The striker was closer ten minutes later when his shot on the turn flew just wide of Brad Friedel's near post.
But in between those efforts, Blackburn had the ball in the Reading net, only for McCarthy to see his effort ruled out for offside.
Morten Gamst Pedersen squirmed his way past Graeme Murty on the edge of the area and unleashed a fierce shot that Marcus Hahnemann could only parry and the keeper was relieved to see McCarthy's follow-up tap-in greeted by an offside flag.
Reading should have been in front on 14 minutes when Nicky Shorey's low cross was pushed out by Friedel under pressure from Seol, the keeper then recovering brilliantly to parry Harper's close-range shot.
And when the home side did find a way past Friedel, they were denied by the woodwork, Sidwell's header from a Glen Little free-kick smacking against the crossbar.
But Reading's increasing dominance produced the lead the home side deserved as Blackburn's creaking defence finally cracked.
Stephen Hunt's clever lob over the top completely exposed the wandering centre-backs and allowed Harper to run free and slot the ball under Friedel.
And it could have been 2-0 in first-half stoppage time when Doyle robbed Andy Todd wide on left and cut across goal, but saw his low shot beaten out at the near post by Friedel.
Blackburn were looking a shambles, but an interval switch in tactics by Hughes almost paid instant dividends at the restart, as Rovers were robbed of an equaliser.
Pedersen played a clever ball through the heart of the Reading defence and McCarthy's well-executed finish was again met with an offside flag - this time wrongly.
McCarthy's hapless afternoon continued when he collapsed in the penalty area after Ibrahima Sonko had stumbled in front of him. This time he was more lucky not to be booked for diving, rather than unlucky not to win a penalty.
But the South African striker completed his remarkable hat-trick moments later when he sprung forward to roll the ball into Hahnemann's net for a third time, only to see the flag raised once more.
McCarthy finally claimed his goal at the fourth time of asking on 64 minutes, this time timing his run to perfection to head home Lucas Neill's inviting cross.
Rovers could have completed a remarkable turnaround seconds later. Bentley's thunderbolt strike was beaten out by Hahnemann and the midfielder's follow-up was also blocked.
Reading, belatedly, reacted and defender Ivar Ingimarsson was unlucky not to see his low half-volley fly either side of Friedel, rather than straight at him.
But the momentum remained with Blackburn and their second-half comeback was completed by a stunning strike from Bentley six minutes from time.
John Oster's first touch after coming on as substitute was an intended pass to Shorey that was easily picked off by Bentley. The midfielder was allowed to run forward into the space left by Shorey and unleash an unstoppable right-foot drive that flew past Hahnemann.