Auckland were never entirely safe, with three points separating the two sides for the last 25 minutes as Manawatu pushed desperately for the breakthrough. The home side might look back and rue the fact they passed up the opportunity for a shot at goal with 15 minutes remaining, choosing instead the ambitious option of going for a try.
The win leaves Auckland undefeated in their two games but they have been unconvincing so far and will need to improve considerably if they are to challenge the likes of Canterbury and Wellington and claim their first title since 2007.
They will also hope Piri Weepu's shoulder injury isn't too bad, with the halfback forced from the field in considerable pain in the 59th minute.
One area they enjoyed dominance was in the scrums, particularly in the second half, but they should have been too strong for Manawatu.
At least the Turbos claimed a bonus point, which was the least they deserved, but they might have imagined more after leading 18-9 after 50 minutes. They dominated the first half as they combined backline endeavour with intensity at the breakdown and scored tries to halfback Nic Stirzaker, who darted in from a scrum 10m from the line, and Cama, who started and then finished a break from their own half.
"For the second week in a row, we were playing in patches,'' Auckland captain Parkes said. "I'm looking forward to the time when we can play for the full 80 minutes.
"I think we were pretty lucky to come away with the points.''
Manawatu 18 (Nic Stirzaker, Tomasi Cama tries; Jade Te Rure 2 pens, con) Auckland 21 (Patrick Tuipulotu, Sean Polwart tries; Simon Hickey 3 pens, con). HT: 15-9.
