Spanish livewire Jota, a summer signing from Celta Vigo, sparked the Bees into life with an 11th-minute opener.
Tottenham loanee Pritchard grabbed the second before the interval and although Simon Cox pulled one back, Douglas scored a late third to send Reading on the short trip back down the M4 empty-handed.
The Royals, having recently been taken over by a Thai consortium, have designs on a promotion push this term but now find themselves below newly-promoted Brentford in the table.
The hosts almost went ahead after just 90 seconds when Alan Judge burst into the penalty area and crashed an angled drive against the outside of the post.
Nick Blackman could have put Reading into the lead moments later with a driving run into the box but his shot was well blocked by home keeper David Button.
And it was Brentford who made the breakthrough when Alan McCormack sent a high cross into the area and, as striker Andre Gray challenged Royals defender Michael Hector, the ball dropped for Jota to tap in from six yards.
Blackman posed Reading’s chief attacking threat and he twice came close to equalising, heading Jordan Obita’s cross over the crossbar before curling another effort narrowly wide.
But it was the Bees who struck again before the break with Pritchard scoring his second goal of the season.
Again Gray was unwittingly the creator, neatly taking Douglas’ square ball past his marker on the edge of the box only to slip on the soggy pitch as he went to shoot.
But the ball this time fell kindly to England Under-21 midfielder Pritchard who drilled a low, first-time shot past Adam Federici and into the net.
Royals boss Nigel Adkins made a double substitution at half-time, throwing on Jamie Mackie and Cox, and the move paid off within four minutes of the restart.
Mackie’s shot from distance looked unlikely to trouble Button but Cox stuck out a boot to divert it past the Bees keeper as the hosts looked for an offside flag which never came.
Reading went in search of an equaliser and Glenn Murray headed over before Button saved from Mackie, but Douglas condemned them to a third away defeat this season when he nodded in Pritchard’s corner with 10 minutes remaining.