The Portuguese striker was a threat all night and - having twice been denied by the woodwork himself - thoroughly deserved to put us ahead just before the break.
Mark Yeates also hit the bar but Forest struck back with 12 minutes left and it could have been worse - goalscorer Marlon King missed the best chance of the night in the final minute.
The crossbar came to Forest's rescue after just seven minutes when Postiga out-muscled John Thompson to reach Yeates' flick, dinked over goalkeeper Pascal Formann only for the ball to bounce back to safety.
Rohan Ricketts volleyed just wide and after a lull in the game, Postiga hit the woodwork for the second time, this time a powerful header from John Jackson's inch-perfect cross.
Phil Ifil impressed in the first half and it was fitting that the 17-year-old full-back combined with Postiga to put us ahead, his cross buried from close range for 1-0 two minutes before the break.
Our best spell of the game came at the start of the second half. Substitute Jamie O'Hara set the tone with a scorcher tipped over by Formann and the keeper gathered safely as Ricketts' drive zipped through a crowd of bodies.
Lars Hirschfeld made his first save of the night after 56 minutes, a decent palm away as Ross Gardner latched onto a defensive lapse, but play was soon down the other end again, a quick break from a Forest corner, a one-two between Yeates and Ricketts and the Irish forward shot into the side-netting.
Yeates was denied minutes later in the best moment of the night. Picking the ball up on the left, Yeates shaped up and curled towards the top right corner from 30 yards only to see Formann's fingertips flick it onto the crossbar and over.
Forest would soon capitalise on their fortune. They equalised on 78 minutes when Craig Westcarr stood up a fine cross from the byline that left King with the easiest of tasks to head home.
Hirschfeld darted out to deny Westcarr five minutes later and then, in the last minute, King and Westcarr combined again only for King to hit Row Z from close range.
Line-ups: Spurs: Hirschfeld, Ifil, McKie (O'Hara, 45), Hughes, Kelly, Mabizela, Ricketts, Redknapp (Barnard, 73), Yeates, Postiga, Jackson. Subs: Eyre, Daniels, Dobson.
Forest: Formann, Biggins, Doig, Stewart (Beaumont, 73) Thompson, Tarka, Cash, Bopp, King, Westcarr, Gardner. Subs: Beaumont, Tynan, Haskins, Bodkin, Hurren.
Forest snatched a draw after Helder Postiga opened the scoring and we rattled the crossbar three times in last night's reserve clash at Stevenage.