An unbeaten 39 from Craig Kieswetter turned the LV= County Championship Division One clash with Durham in Somerset's favour after day three at Chester-le-Street.
Only 35 overs were bowled because of poor light, but Somerset reached 96 for two in their second innings and need a further 139 to win in what is forecast to be improved conditions on the final day.
There was a hint in the ease with which Durham's last man Chris Rushworth scored 18 that batting was not as hazardous as when 18 wickets fell in 78 overs on Thursday.
Unfortunately for Durham, Rushworth went in to face the day's fifth ball when play began at 1.40pm after Phil Mustard, the main hope of a substantial boost to the total, was run out.
He turned Alfonso Thomas to fine leg and risked a second run, but failed to beat Jamie Overton's excellent throw.
Somerset chose Overton to bowl rather than Peter Trego or Steve Kirby. Swing and seam had done the damage, but the teenager opted for an aggressive approach to no avail.
Graham Onions appeared in little trouble, but Rushworth surrendered when he tried to pull Thomas (four for 29) and gave wicketkeeper Kieswetter his fifth catch of the innings and his eighth of the match behind the stumps as Durham were all out for 116.
Somerset began their pursuit of the victory target in confident fashion, taking 30 off the first six overs, including ten off Rushworth's third.
Arul Suppiah dominated the scoring after Marcus Trescothick opened up by straight driving Onions' fourth ball for four.
Onions had Suppiah lbw for 17 then after a 20-minute break for bad light, Kieswetter dominated a stand of 43, hitting two of his five fours off successive balls from Onions.
Trescothick was twice beaten by Callum Thorp, who conceded ten runs in nine overs, but the Somerset captain appeared to have got through a sticky patch before Ben Stokes struck after replacing Onions.
Trescothick played back to Stokes' fifth ball and got an inside edge into his stumps to depart for 22, but James Hildreth (12 not out) kept Kieswetter company until the gloom closed in again.
