It took 16 minutes for the deadlock to be broken, and it is a moment that the Bluebirds will want to forget swiftly due to a blender made by Paterson.
The mistake came from a Reading corner, which drifted into the box and in an attempt to clear with no real danger around him, Paterson headed the ball into his own net.
A few minutes later, Yann Kermorgant came close to putting the Royals two goals to the good inside the first 22 minutes, but after latching on to the end of Sone Alum's cross, the striker headed wide.
Joe Ralls tried to make things happen for the visitors when he unleashed a shot from distance, but Vito Mannone was alert as he made the stop and then quickly denied Nathaniel Mendez-Laing from curling the ball into the top corner.
Cardiff struggled to get a foothold in the game and they were punished just before half time when Barrow grabbed the ball on the edge of the box and hit a shot that was deflected into the back of the net.
After the interval, Neil Warnock's side tried to get themselves back into the contest through Junior Hoilett, who got on the end of Mendez-Laing's cross before directing a bouncing header over the crossbar.
The frustration of the evening soon got to the Cardiff boss as he was sent to the stands by the referee for reacting angrily to a decision that went against his team.
Strangely, Warnock's exit seemed to galvanise the players as Bennett pulled a goal back for the visitors in the 83rd minute by volleying the ball past the keeper.
The move began with Hoilett, who charged to the byline before cutting the ball back towards the box to find his teammate, who put Reading under pressure in the closing stages of the contest.
Cardiff kept pushing and eventually snatched an all-important goal when the ball was delivered into the box and found Tomlin, who reacted quickly by hammering it past the keeper.
In the end, the points were shared between the two clubs, which leaves the Bluebirds second in the Championship table, four points behind leaders Wolverhampton Wanderers, while Reading sit 14th, 10 points adrift of the playoff places.