Moments later Patrick Cox was sent off for bringing down Andy Mangan when he was clear on goal, the striker then blowing a great headed chance.
With minutes left Obeng fouled Chris Flood in the box and Tubbs stepped forward nervelessly to all but end Wrexham's fading play-off hopes.
Wrexham manager Dean Saunders:"It definitely wasn't a penalty, the referee has got to be sure when he gives a decision like that with two minutes to go.
"I'm getting used to it at this level, I don't think there's anything I can do about it.
"I haven't been as disappointed as that since I've been at the club.
"We totally from dominated start to finish and had about 10 chances on goal in the first half and 10 in the second and not put the chances away.
"I feel like there's so much right with us and we had the three points in the bag. To come away with one point - I'm just sick.
"Sometimes it feels like the world's against you, but I'm a fighter. I'll just pick myself up, pick the players up and on we go again."
Salisbury: Bittner, Clohessy, Ruddick, Cox, Bush, Flood (Osman 90), Adelsbury, Connolly (Gray 77), Clarke, Sinclair (Anderson 31), Tubbs. Subs Not Used: Pryce, Monhon.
Sent Off: Cox (71).
Booked: Ruddick.
Goals: Tubbs 89 pen.
Wrexham: Russell, Spann (Obeng 46), Westwood, Assoumani, Mike Williams, Holden, Smith, Fleming, Baynes, Jones (Anoruo 90), Mangan. Subs Not Used: Maxwell, McCluskey, Wolfenden.
Booked: Smith, Jones.
Goals: Smith 69.
Att: 948.
Ref: Kevin Johnson (Somerset).
Source: BBC Sport
Source: BBC Sport