The home side's best chances fell to Andrew Cooper, who caused problems with his speed and went close with stinging shots in either half.
Tauranga City United captain Sam O'Regan took much of the responsibility for the loss on his own shoulders, but for the most part he and Raymond How marshalled a back division that coped well with the high-flying Auckland side.
"Sometimes we push the long ball a little too much - down to the boys at the back - but we are far better than that," O'Regan said.
"Credit to the other team but I think that was our game to lose and individual mistakes from me have cost us.
"As the game goes along at 1-0 you open up a little bit, but I think that was our game."
O'Regan said the Chatham Cup campaign had been a welcome distraction from the promotion race and he was proud to have helped bring a high-quality game of football to Links Avenue.
He did not believe the absence of coach Duncan Lowry played a part in the loss.
"We're grown men and we all know what needs to be done. I don't think that was the difference. People can look at it and think because we're missing Duncan and certain things come into it, but it was individual mistakes.
"I'll hold my hand up and say I might have switched off and obviously the difference between the leagues is that up there you don't really get a second chance. There's only so much keepers can do."
Onehunga Sports 2 (Josh Ming, Sean Lovemore) Tauranga City 0