Bira Dembele's 21st-minute header in his third start for Graham Westley's side deservedly put Boro in the lead while Tubbs missed a second-half penalty for the hosts at the Broadfield Stadium.
But Tubbs made amends at the death after getting on the end of Dannie Bulman's ball and firing home past the helpless Chris Day.
In an scrappy opening half, Michael Doughty's header found Francois Zoko and he was left one-on-one with Paul Jones but Town's keeper pulled off an incredible save to keep the scores level.
One minute later Stevenage - going into the game with back-to-back wins for the first time this season - opened the scoring when Jimmy Smith's cross found Dembele and the defender buried his header.
Just past the hour mark Jamie Proctor and Mike Jones were involved in some excellent build-up play on the right before the former put in a dangerous ball but Tubbs failed to get on the end of the teasing cross.
Tubbs had a great opportunity to level the scores after Dembele was adjudged to have fouled Proctor but his spot-kick was excellently saved by Day.
The striker, on-loan from Bournemouth, had the last laugh when he smashed home to make it unbeaten in seven for John Gregory's men.
Crawley are up to 13th in the table while Stevenage stay 23rd, although they are only three points from safety with a game in hand.