After winning the toss and choosing to bat, the visitors were bowled out for 296, with Berg claiming five for 58 to claim, his seventh five-wicket haul in first-class cricket.
Northants then closed on 26 for two in reply, losing skipper Ricardo Vasconcelos and nightwatchman Simon Kerrigan, but new signing Will Young was still there at the close, unbeaten on 10 from 44 balls.
The Leeds-born all-rounder struck in successive balls to remove Vasconcelos and Kerrigan, following up his quickfire 51 which had guided Yorkshire from the choppy waters of 206 for seven.
Rising star Harry Brook top scored for the visitors with 84, sharing a stand of 131 with Dawid Malan after Berg had given Tykes skipper Steven Patterson reason to regret his decision to bat with three wickets in a typically probing opening spell.
The elder statesman of the new-ball art was indebted to debutant Young for the wicket of Adam Lyth, the New Zealander diving to his right at second slip to clasp the edge inches above the turf.
Berg, then induced a thin nick through to keeper Lewis McManus to send George Hill packing for a duck.
It should have been even better two balls later when Malan edged another ball which moved away off the seam, only for Vasconcelos to shell the most routine of slip catches.
Undeterred, Berg struck again in his sixth over when Sri Lanka Test skipper Dimuth Karunaratne gave McManus more catching practice, but the dropping of Malan was to haunt the hosts for some time.
Karunaratne’s demise brought Brook to the crease fresh from his unbeaten half-century in last week’s win over Gloucestershire.
The 23-year-old right-hander, who made his T20 international debut on the West Indies tour this winter, also has history with Wantage Road, having made a century in Yorkshire’s win in the same fixture a year ago and he was quickly into stride, a savage pull in front of square off Aussie debutant Matt Kelly an early highlight.
Meanwhile, Malan, a scapegoat for England’s post-Ashes red-ball reset, was making the most of his early reprieve as Luke Procter made the mistake of feeding his trademark cover drive.
The duo gorged on Kerrigan too in the run up to lunch, Brook hammering the spinner over mid-wicket for six. The 100-partnership came soon after the resumption, but Berg returned to pin Malan lbw.
Nevertheless with Brook continuing serenely on the visitors were in charge at 203 for four before the game took another turn.
Ben Sanderson, who’d not been at his best with the new ball, bowled Harry Duke before grabbing the prize wicket of Brook, both off the inside-edge and with Rob Keogh castling Dom Bess in the intervening over, Yorkshire suddenly found themselves pegged back.
Thompson though fought back aggressively, clattering a six into the advertising hoardings in a 69-ball 50, his fourth in first-class cricket, before Kelly removed him and Patterson in successive balls.
Fittingly, it was Berg who then bowled Harris Rauf to complete his fifer, leaving Yorkshire four runs shy of a third batting point.
Vasconcelos dispatched the first ball of the host’s reply to the boundary, but Northamptonshire were largely circumspect, at one stage absorbing 36 balls without scoring.
Their bid to reach the close unscathed was undone by Thompson (two for 13) who trapped Vasconcelos in front before having Kerrigan taken at slip for a first ball duck.