Counties-Manukau opened the scoring in the fourth minute when first five-eighth Baden Kerr kicked a penalty from 26m after Taranaki referee Richard Kelly ruled Magpies winger Tino Nemani offside, then landed a second penalty from a similar position.
Waenga opened the hosts' account in the ninth minute with a penalty from 35 metres out.
Chiefs utility back Tim Nanai-Williams scored the first try for the Steelers in the 11th minute after hitting the line at pace on to a well-timed pass from Kerr, who slotted the conversion. But three minutes later Waenga landed another penalty.
Halfback August Pulu scored the Steelers' second try in the 15th minute when the visitors applied quick hands under an advantage call from Kelly. Kerr slotted the conversion to put his side ahead 20-6.
Waenga landed his third penalty from 32m in the 20th minute, only for Waenga to succeed with his fourth kick minutes later to have the hosts trailing 20-12.
Kerr nailed a 28th minute penalty from 39m but Waenga matched Kerr's five from five effort with a 33rd-minute penalty after Steelers prop Simon Lemalu was sinbinned for infringing at the breakdown.
Magpies hooker Hika Elliot scored a try after continuous pressure from the hosts' pack as the halftime whistle sounded. Waenga's conversion had the Magpies trailing 23-22.
Sherwin Stowers scored the Steelers' third try with a spectacular solo effort. Kerr landed the conversion, but Waenga closed the gap to 30-25 with his seventh consecutive success at goal.
Magpies pressure and quick ball saw centre Tua Saseve score the hosts' second try in the 59th minute. Waenga couldn't convert but broke the deadlock in the 71st minute with a try after an Andrew Horrell break. Waenga landed the conversion.
Hawkes Bay 37 (H Elliot, T Saseve, D Waenga tries; Waenga 2 con, 6 pen) Counties Manukau 30 (T Nanai Williams, A Pulu, S Stowers tries; B Kerr 3 con, 3 pen). Halftime: 22-23.
