It came on the hour from one of the Forest breakaways that had been a constant threat to the Royals. Lewis McGugan used his pace and strength to hold off Marek Matejovsky before sending a left-foot shot past keeper Adam Federici
Both sides had been struggling to find their form going into the match. Reading had won just once in five games, without any Reading player scoring and Forest had gathered only one point from the last 15 available.
In an effort to end the run Royals manager Steve Coppell brought Czech international Matejovsky in for his first start of the season, dropped Leroy Lita in favour of Noel Hunt and brought in Brynjar Gunnarsson for Kalifa Cisse.
Forest were without suspended skipper James Perch and injured players Guy Moussi, Joe Garner, Julian Bennett and Arron Davies.
Inside the second minute Reading had a wonderful chance to take a lead which would totally have changed the face of the game. Kevin Doyle sent in a cross from the left and while the defence concentrated on Noel Hunt the ball ran free to an unmarked Jimmy Kebe.
With plenty of time to spare Kebe dragged his shot wide of the left-hand upright. Four minutes later Reading again came close when Brynjar Gunnarsson headed a Stephen Hunt free-kick just over the bar.
Chris Cohen caused Reading a fright when he put Robert Earnshaw clear, but Alex Pearce, who was solid throughout, managed to make a superb tackle to prevent him getting a shot in.
Although they were on the defensive for long spells Forest did pose a threat from breakaways and shortly after coming on as a substitute Gareth McLeary tested Federici with a shot, then Earnshaw fired just over the bar.
Federici prevented Forest taking the lead in the 58th minute when he leapt to his right to tip away a goalbound shot from Cohen.
Two minutes later Reading boss Steve Coppell made the change Reading fans had been calling for. He took off the struggling Kebe and put Jay Tabb on the right side of midfield. It was Tabb's first appearance since signing from Coventry for £300,000 in January.
However, almost immediately Forest got the goal that was to earn them victory.