The visitors eased into a 2-0 lead inside the opening 13 minutes at the City Ground courtesy of Pavel Pogrebnyak and Kaspars Gorkss, only for Forest to level through Simon Cox and Darius Henderson.
However, teenage winger Obita had the final say as he snatched all three points for Nigel Adkins' men - who had ex-Forest full-back Chris Gunter sent off late on - with 16 minutes remaining.
Pogrebnyak gave the visitors a deserved lead in the eighth minute with a typical poacher's finish after good work down the right by former Forest winger Garath McCleary.
And Reading did not have to wait long to double their advantage, as Latvia international Gorkss planted a firm header past Karl Darlow from a superb Danny Guthrie delivery just four minutes later.
Forest responded well, though, and Cox pulled one back five minutes before the break as he converted Jamie Mackie's cross from close range.
The hosts came out on the front foot after the break, and they were level after 60 minutes when Cox sent Henderson through and the striker finished well.
Mackie then went close once again as he cracked a shot against the upright soon after as Billy Davies' team pushed for the win.
But it was Reading who grabbed all three points through Obita, as he took advantage of some slack defending to lift Adkins' side above Forest, who slip to sixth.
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