Bolton Wanderers 1 Blackburn Rovers 2
A late second-half substitute, the former Wigan hitman pounced to make sure Mark Hughes' battling side battled back from 1-0 down to triumph.
Just as it looked as though a draw was on the cards, the out-of-favour striker beat Bolton keeper Jussi Jasskenlainen with a sweet 90th minute strike.
It was rough justice on Gary Megson's brave side who had taken a 42nd minute lead courtesy of a superb volley from influential skipper Kevin Nolan.
But a 53rd minute equaliser from Christopher Samba gave Rovers hope and they took their chance when Roberts came on to stun the home side at the death.
Bolton had the first chance of the game and Lubomir Michalik should have done better from close range. The Solvakian defender unleashed a left-foot shot from ten yards out, but Ryan Nelsen made a smart block to avert the danger.
In the ninth minute Blackburn midfielder David Bentley tried his luck with an ambitious 30-yard drive, but his powerful right-footed shot was well saved by Jaaskelainen.
Former Bolton target David Dunn was then clattered by Ivan Campo and from the resulting free-kick Tamir Cohen floated a delicious pass to the unmarked Kevin Davies, but the striker saw his close-range shot saved by Brad Friedel.
Six minutes later Campo broke clear of his marker and let rip with a right-foot shot, but his effort caused Friedel no trouble.
An inswinging corner from Morten Gamst Pedersen caused problems midway through the half with Bolton forced to punch clear.
The deadlock was eventually broken when Nolan found space on the left-edge of the area after a inch-perfect pass from Joey O'Brien and fired past Friedel with an outstanding volley.
It was his fourth goal of the season as Bolton went in search of revenge after losing 2-1 to Rovers at the Reebok last season.
Two penalties from Benni McCarthy did the damage that day, although the recently departed Nicolas Anelka netted a late consolation for the home side.
Blackburn came close to levelling a minute before the break, but Roque Santa Cruz headed over from Pedersen's perfectly-weighted cross.
Two minutes into the second half Santa Cruz had another good chance to level matters, but from Pedersen's chested down pass he saw his powerful shot well-saved by Jaaskelainen.
But the visitors kept pressing and deservedly squared matters after sustained pressure.
An inswinging cross from Bentley found Samba and he rose tallest to direct a powerful past the stranded Jaaskelainen.
Dunn made a superb last-ditch saving header close to the hour mark as a dangerous cross from Nolan looked goalbound.
Pedersen came within inches of giving Blackburn the lead in the 70th minute, but from close range failed to net his first goal of the season.
Nolan then went close for Megson's side as they went in search of a late winner. He received the ball from substitute Christian Wilhelmsson, but failed to hit the target.
But for all their hard work Megson's men were hit with a sucker-punch as Roberts beat Jaaskelainen with a clinical finish from 20 yards out.
It could have been 2-2, but Gavin McCann's fierce right-foot shot was blocked by Samba moments before referee Mike Dean blew his whistle for full-time.