Trent Copeland claimed 4-49 as Northamptonshire reduced Hampshire to 149-5 on a shortened second day of their Division Two clash at Wantage Road.
Having been put into bat after the opening day had been washed out, Hampshire were indebted to an unbeaten 57 from Liam Dawson before bad light brought about an early finish.
Australia paceman Copeland was the star for Northants, giving the reigning Division Two leaders the upper hand in what is his penultimate LV= County Championship game before he returns home.
However it was fellow opening bowler David Willey who struck the opening blow, dismissing Hampshire captain Jimmy Adams with the fourth ball of the match.
Adams' openining partner Michael Carberry faired slightly better, reaching 10 before he was caught at second slip by David Sales off Copeland.
Having crawled to 30-2 by lunch, the visitors lost James Vince (eight) in the fourth over of the afternoon when he was trapped lbw by Copeland, who then switched ends to pin Sean Ervine leg before for 26.
The fifth-wicket pair of Dawson and Adam Wheater then moved Hampshire on to 114-4 before bad light forced the players off just before tea.
Dawson completed a watchful half-century when play resumed and by the time conditions ended proceedings for the day with 25 overs still scheduled, he had hit eight fours in his 179-ball stay.
Wheather, though, perished in the gloom, Copeland ending the former Essex wicketkeeper's innings on 40 with a delivery that hit off stump.