The Royals' unbeaten run of eight ended at a ground where Brentford have not lost in more than six months - two goals in three minutes at the end of the second half setting Brentford on their way to all three points.
Reading had hit the woodwork through George Evans towards the end of an evenly-contested first half, but Josh Clarke and then Lasse Vibe handed Brentford an unassailable advantage going into the break with close range finishes.
A wide open second half promised more goals and Maxime Colin hammered home a third, while Kermorgant had a header cleared off the line and Harriott was denied by the post. Substitute Quinn won a penalty which Kermorgant coolly placed high past the dive of Bentley to pull one back just after the hour, but time was against a Reading fight back and Hogan found the back of the net to add a fourth near the end.
Jaap Stam made one change to the side that beat table-topping Huddersfield at the weekend, replacing Danny Williams with George Evans in midfield. Liam Kelly was drafted into the squad to join fellow Academy graduates Dominic Samuel and Tennai Watson on the bench at Griffin Park.
In the first minute it took a great sliding challenge from skipper Paul McShane to prevent Scott Hogan getting a very early shot away after the in form striker was slid in with a defence-splitting pass from
Reading quickly settled into their passing play, yet it was the Bees who threatened again after quarter of an hour - Joey van den Berg fouling Vibe 22 yards out and Bjelland arcing a well-struck set piece around the wall and into the side netting.
A couple of successive Swift corners gave the Royals their first chance to get sight of Daniel Bentley's goal, but the Bees defended both well. Then Harriott worked a shooting position on the edge of the box, but skied the ball high over the crossbar.
Brentford were looking dangerous and it took a perfectly-timed sliding challenge from Van den Berg on Vibe to prevent the striker from getting a shot away inside the Royals box.
Former Bees loanee Swift took aim from 25 yards out but dragged his effort well wide on this occasion, then he came close to getting on the end of a lovely cross from Harriott but the ball sailed behind for a goal kick.
Swift spread the ball wide to Beerens with ten minutes of the first half left, but the winger's swerving strike whistled through the night sky and into the arms of Bentley in the Brentford goal.
Then, Reading hit the post. Beerens won a free kick on the right, Swift delivered it into the box and Evans glanced it against the base of the left upright with his head. McShane and Kermorgant scrapped to try to get another meaningful shot away, but the hosts hacked it clear eventually.
But moments later, Brentford took the lead. A move that began down the right led to a low cross into the middle which was dummied, then helped on to Josh Clarke who fired high past Ali Al Habsi from 8 yards out.
And before half-time, the home side had a second. A low Hogan cross into the middle from the left found the run of Vibe who got his toe to it first inside the six yard box and he stabbed the ball under Al Habsi from close range for 2-0.
The Royals came close to pulling one back before the interval. Van den Berg swept the ball wide to Beerens who forced Bentley into a fine low save and Kermorgant came close to directing the ricochet into the net only for a Brentford leg to do enough to keep it out and concede a corner.
Half-time: Brentford 2-0 Reading
Within the first four minutes of the second half, the Royals passed the ball patiently at the back and created a golden chance. Harriott found Gunter in space on the right and his deep cross was headed past Bentley by Kermorgant, but John Egan on the line somehow cleared the Frenchman's effort.
That woke the home side up and two great saves from Al Habsi kept the game alive, first denying Hogan who raced through one on one with the keeper, then flying to his left to push away a fierce effort from the same man who had found space to let fly from range.
The game was wide open and the next goal was going to be important in the context of the game. And Brentford had a third when Colin slammed home from the right side of the Royals box.
Reading had hit the post and seen an effort cleared off the line, and Harriott was thwarted by the woodwork again when he stabbed a right-footed effort past Bentley and flush against the right post.
Then, just after the hour, Quinn was tripped inside the box as he scampered after a Swift throughball and referee Oliver Langford pointed to the spot. Yann Kermorgant stepped up and lifted the ball high into the Brentford net to pull one back.
Kermorgant threaded a ball into Quinn inside the box, but the offside flag was raised against the Royals midfielder before he could get a shot away. Next, Evans wound up a first time strike from distance that sailed high and wide.
Joseph Mendes and Dominic Samuel were thrown on with six minutes remaining, but Brentford added a fourth moments later when Hogan sprung the offside trap to collect a pass, turn and slot wide of Al Habsi's dive and inside the bottom right corner.
Full-time: Brentford 4-1 Reading
Brentford: Bentley, Colin, Dean (c), Egan, Bjelland (Barbet 69), Clarke, McCormack (McEachran 83), Yennaris, Sawyers, Vibe (Kaikai 87), Hogan.
Unused subs: Bonham, MacLeod, Saunders, Hofmann.
Yellow: Dean, McCormack, Bjelland, Yennaris
Goals: Clarke (40), Vibe (43), Colin (57), Hogan (86)
Reading: Al Habsi, Gunter, Obita, McShane (c), Moore, Van den Berg (Quinn HT), Evans, Swift, Harriott (Samuel 84), Beerens (Mendes 84), Kermorgant.
Unused subs: Jaakkola, Watson, Gravenberch, Kelly.
Yellow: Van den Berg, Swift
Goals: Kermorgant (63 pen)