Somerset's push for a first County Championship title was held up by Liam Dawson's century as Hampshire recovered from 24-5 on day one at the Ageas Bowl.
Lewis Gregory took three early wickets to leave Hampshire deep in trouble after electing to bat.
But England all-rounder Dawson led the recovery with 103, and Keith Barker hit 40 before they were dismissed for 196.
Kyle Abbott then struck twice to leave Somerset 30-2 in reply when bad light forced an early close.
The South African paceman trapped India opener Murali Vijay leg before and then, after a short delay for bad light, bowled Steve Davies with one that nipped away before play was finally called off with the match finely poised.
Somerset began the penultimate round of games eight points clear of Essex at the top of the Division One table.
And while their title rivals were delayed starting their game with Surrey because of bad light at Chelmsford, Somerset were soon into their work and made the perfect start after losing the toss to pick up maximum bowling points.
Gregory struck with the third ball of the game as Felix Organ edged to James Hildreth at first slip, before Josh Davey bowled Tom Alsop.
Gregory then had Sam Northeast caught at gully and bowled James Vince through the gate to leave Hampshire 18-4, and they were 24-5 when Ian Holland edged Craig Overton to Vijay at second slip.
Dawson, who had made six half-centuries in the Championship this summer before this game, began the rebuild with Aneurin Donald and Lewis McManus.
But it was his eighth-wicket stand of 92 with Barker that helped steer Hampshire towards a potentially competitive total on a pitch that has offered plenty of movement with the new ball, and at a ground where neither side mustered 200 in the first innings of last week's win over Surrey.
Somerset will now look towards captain Tom Abell and the experienced Hildreth to give them a solid platform when play resumes on Tuesday as they look to better Hampshire's total and build a first-innings lead.