Unknown Australian import Trent Lawford shared the new ball with Boult.
Scott Kuggeleijn has impressed all series with his pace and looked decidedly slippery downwind.
He had a spectacular catch dropped catch off his bowling by Corey Anderson, from Michael Guptill-Bunce, but two balls later Kuggeleijn knocked his off stump over to have the Aces 22/1 in the third over.
Anderson threw down the stumps to run out skipper Nicol for a duck in a key moment next over to give the Knights the early momentum.
Kuggeleijn bowled Glenn Philips to have the Aces reeling at 41/3 in the seventh over, with strike-rate champion Mark Chapman joining Jeet Ravel to try to resurrect the innings.
Boult worked out Ravel with a smart piece of bowling to have the Aces 54/4.
Ben Horne, nephew of Knights assistant coach Matt Horne, joined Chapman in a crucial coupling for the Aces.
Boult should have had another wicket in the 11th over but keeper Tim Seifert took too long to get the bails off with Chapman well beaten.
Boult finally snared Chapman for 30 after a great catch by debutant Peter Bocock with the Aces 89/5 with 15 overs gone.
Boult's 2-21 off four overs was fitting return for a fine spell.
Horne played well for 39 off 27 balls but the Aces struggled through to 142/6, helped by consecutive sixes off the last two balls bowled by Daryl Mitchell.
Black Caps Dean Brownlie and BJ Watling opened for the Knights chasing 7.16 runs per per to win.
The pair took 16 off the opening two overs and 36 off five in a solid start, with wickets in hand the key to any run chase.
The 50 came up in good time in the seventh over with key spin bowlers Tarun Nethula and Nicol targeted by captain Brownlie.
He went to 50 off 30 balls with his third big six as the Knights roared away to 83/0 off nine overs.
Brownlie was finally out for 54 at 87/1 replaced by big-hitting Black Cap Corey Anderson.
Watling stroked the ball effortlessly around the wide-open Bay Oval outfield, making a fine unbeaten 54 to anchor the nine-wicket victory.
The Knights host the Canterbury Kings at Bay Oval from 4pm tomorrow.Auckland Aces 142/6 (Ben Horne 39; Jono Boult 2-21, Scott Kuggeleijn 2-28, Trent Lawford 1-26) lost to Knights 143/1 off 15.3 overs (Dean Brownlie 54, BJ Watling 53*, Corey Anderson 23*)