Somerset 534 for 7 (Overton 97*, Van der Merwe 94*, Abell 79) lead Hampshire 338 (Ervine 103, McLaren 61, Leach 6-108) by 196 runs
Craig Overton was left three runs short of a maiden first-class century when play ended four overs early on the third day of the Specsavers County Championship match with Hampshire at Taunton.
He faces an anxious overnight wait to see if Somerset captain Chris Rogers declares before he has the chance to achieve the landmark.
He said: "I honestly don't know what we are going to do. Of course, I would like the chance to bat on, but in the end the team must come first and I'll go with whatever the skipper decides. I was disappointed when we came off, but the umpires had made it clear the previous over that there would not be much more play."
Overton and Roelof van der Merwe, who was also seeking his first hundred for Somerset, were unbeaten on 97 and 91 respectively, with their unbroken eighth wicket stand worth 164, and Hampshire were looking at a last day survival mission.
Half-centuries from Overton, van der Merwe, Lewis Gregory and Jim Allenby batted Somerset into a strong position. By the close, the hosts had reached 534 for 7 in reply to 338, having begun the day on 257 for 5, and led by 196 for on a pitch still offering turn and occasional bounce for the spinners.
After morning drizzle had forced an early lunch, play got underway at 1pm, with Allenby unbeaten on 37. He went on to a 116-ball half century before the second new ball was taken at 291 for 5.
Nine runs had been added when Allenby, on 56, looked to pull a leg-side bouncer from Ryan McLaren and either edged or gloved a catch to wicketkeeper Lewis McManus.
Gregory and van der Merwe were soon making further inroads into Hampshire's first innings total, with Gregory hitting seven fours in moving to a handsome fifty off 79 deliveries.
The pair were almost involved in a comical run out with the score on 302, first both racing in one direction and then the other after van der Merwe had called for a quick single. Sadly for Hampshire, the ball was fumbled and they failed to capitalise.
It proved costly as Somerset moved on to 370 before Gregory edged a drive to slip off leg-spinner Mason Crane and departed for 61.
Overton survived a chance to first slip off David Wainwright early in his innings, but in general the Hampshire spinners lacked the consistency in line and length to profit from the dry surface.
There were no more opportunities as van der Merwe reached his half-century off 78 balls, with 2 fours and 2 sixes, and Overton followed from 93 deliveries, with 5 fours and a six.
It was van der Merwe's best first class score for Somerset and Overton's best of the season. By the time bad light interrupted play at 4.50pm both were batting with consummate ease.
A resumption at 5.35pm saw Overton smash Will Smith for 4,4,6,6 in an over that cost the off-spinner 21.
Hampshire looked likely to be spared more fireworks when the umpires decided the light was too poor after just three of the 15 overs they had decreed were left in the day.
But at 6.10pm the players took the field again, with six overs due to be bowled. When their stand reached 132 Overton and van der Merwe claimed a Somerset record partnership for the eighth wicket against Hampshire, beating the 131 stand of Ernie Robson and Lionel Palairet at Southampton in 1896.
The day ended strangely as van der Merwe summoned the 12th man onto the field with four overs to go. As they were talking, the umpires decided no further play would be possible and Overton was left standing with head bowed so close to an important personal milestone.