Hampshire will need to find three wickets to secure victory on the final day of their Championship clash after they were held up by the Somerset tail.
Declaring their first innings on 627 for nine at lunch, with Sean Ervine falling just two runs short of becoming the third centurion of the innings, Hampshire then made significant inroads into the Somerset batting line-up after lunch.
James Tomlinson and Chris Wood struck early blows to remove the openers.
And wickets fell at regular intervals as the Rose Bowl outfit sensed a win with a day to spare.
When Peter Trego was dismissed to leave the score at 132 for six, it seemed only a matter of time before the game was wrapped up.
But Alfonso Thomas (79 not out) and Craig Meschede (53) put on a stand worth 134 for the seventh wicket – only for Dimi Mascarenhas to remove Meschede in the final over of the day.
That left Somerset at 266 for seven – still 157 runs behind – with one day’s play left for Jimmy Adams’ side to wrap up three wickets and boost their ailing hopes of avoiding relegation.