The game was seemingly petering out at 2-2, killed by an England style spate of substitutions, with Pardew fielding a variety of academy stars.
Blackman's late net-busting strike is sure to push his claim for a first team spot. Indeed, the youngster will surely become a fans favourite at Griffin Park as this was a victory the Brentford supporters sorely wanted, still hurting after being denied an automatic promotion spot by Reading just over a year ago.
Early in the game the Royals had raced into a two goal lead thanks to goals from Scott Murray and Nathan Tyson.
Murray, making his Royals debut, had his name on the scoresheet by the fifth minute. Signed from Bristol City for £650,000 a week ago, he hit a low drive from twelve yards following a defensive scramble pre-season games are famous for.
With the Brentford defence still seemingly on their summer holidays, Nathan Tyson doubled the lead five minutes later. A cross from youngster Gary Middleton was flicked on by Henderson for Tyson to smash home.
Middleton, a product of the Reading Academy, played an impressive ninety minutes at left-back, proving that he is more than capable of covering at left-back should injury or suspension hit Nicky Shorey, one of the first names on Alan Pardew's team sheet.
Tyson and Henderson both had chances to leave the Bees further adrift but failed to capitalise on them.
After a quickfire opening ten minutes the game cooled slightly until the game hit the twenty minute mark, when it re-ignited as Brentford levelled the scores in their own explosive ten minute spell.
Bees forward Mark Peters, formerly of Southampton, chipped in a magnificent effort from the corner of the box, leaving Jamie Ashdown with no chance in the twenty-second minute.
Seeing a way back into the match, Willy Downes' side laid siege on the Reading goal. Leo Roget, formerly on loan at Reading, had a twenty-yard strike repelled by Ashdown.
The Griffin Park side finally got their second goal just after the clock had moved past the thirty minute mark. Jay Tabb capitalised on a great through ball from Kevin O'Connor to level the game.
Both sides continued to press forward, and for a while at least it looked as if the game could have ended at about 9-9. Darius Henderson had Reading's best effort of the remainder of the first half but his twenty-yard blast went over the bar.
Surprisingly both manager's entered the second half with unchanged line-ups. Early in the second period Steve Sidwell had his shot stopped by Paul Smith in the Brentford goal.
Cometh the hour cometh the man. Actually, cometh many of them. A whole series of substitutions ensued with the game going rapidly downhill. As radio commentators described, the early match team-play came to an end at the expense of individual-play, as reserve team players aimed to catch the eye of their respective managers.
Darius Henderson aimed to catch the eye of Pardew as he was moved to centre-back. His display at the back can't have failed to have caught the attention of the Reading manager. We suspect that it is a move that won't be repeated. Darius proved he is not a closet centre-back, regularly moving out of position in a bid to move with the attack.
Amongst the substitutional debris, Lloyd Blackman arose to blast his sensational winner, fit for a much higher stage than a poxy pre-season friendly.
Andre Boucard, currently on loan at Peterborough, made an appearance for Reading in the second half and certainly impressed. The skillful youngster's attacking wizardry nearly created an opening but a Reading forward failed to pounce on the chance.
Louis Soares impressed also with some similar creative flair. But again, unfortunately, the final product was not quite there.
Despite the result Alan Pardew will take a lot of positives out of the game, namely the performances of the academy players who came on, none of whom looked out of their depth.
TEAMS: Reading: Ashdown, Middleton, Newman (Soares), Williams (Davies), Castle (Howell), Watson (Boucard), Sidwell (Gamble), Savage (Fashanu), Murray (Notto), Henderson, Tyson
BRENTFORD: P Smith, Dobson (Allen-Page), Somner (Thomas), Roget, Sonko (Traynor), Tabb (Hutchinson), J Smith (Buckley), Peters (Fieldwick), Frampton, Evans (Hunt) and O'Connor (Blackman)