In the second half the Bush forwards dominated, laying a platform in possession and territory from which Rupeni Tamani crossed for a try, converted by Jackson Clince.
Two dropped goals from half back Jordan Bennett-Davis saw Bush take a deserved 19-15 lead but the final result swung on two late Bush kickable penalties, both of which flew wide.
Bush were made to pay when Wiremu Grace dotted down wide out almost on full time, to give Wairarapa the victory.
Bush flanker Johan van Vliet had a strong game and Wairarapa lock Gareth van Dalen was secure in the lineout and put in some telling runs.
Hooker Ihe Namana had a strong game for Wairarapa in defence while James Goodger impressed with his workrate.
Wairarapa coach Stevie Thompson was a relieved man after the final whistle.
"They took us on up front and were outplaying us" he said. "But the game is over the full 80 minutes. We started well but then fell away, but overall it was a gutsy display considering this was their second game of the weekend".
Wairarapa-Bush coach Mark Rutene and assistant Paddy Gough were sideline, assessing the action.
"We're still looking at the midfield mix in particular," said Rutene. Other positions possibly up for grabs in the Heartland squad included hooker and the quest for a third prop.