Liam Dawson gave Hampshire hope of salvaging something from their game with Somerset with a defiant century at the Rose Bowl yesterday.
The 21-year-old England Lions player was unbeaten at the end of the third day on 103 as Hants moved to within 16 of making the visitors bat again at 212 for three.
But the home side will need to dig deep if they are to avoid defeat after another day dominated by Marcus Trescothick.
The former England opener, 193 not out overnight, went on to complete the fourth double century of a distinguished career as Somerset built a first-innings lead of 228.
Somerset resumed 120 ahead at 405 for five in their first innings and were eventually all out for 513.
Trescothick went on to make 227 in a fraction over eight hours from 376 balls in an innings which included three sixes and 32 fours.
The 35-year-old was sixth out at 493 when he drove tenacious left-arm spinner Danny Briggs to the covers, where Dominic Cork completed the catch.
Briggs made the most of his breakthrough by finishing off the Somerset tail, having Jos Buttler leg before, sweeping for an innings of 61 which included 12 fours.
David Griffiths had Gemaal Hussain caught at the wicket at 503 and then Briggs finished it off either side of lunch by dismissing Steve Kirby and Charl Willoughby in quick succession.
Briggs, the only Hampshire bowler to escape heavy punishment on an easy-paced wicket, finished with figures of five for 79 from 38 overs.
Hampshire faced a daunting task but Dawson and Jimmy Adams found batting just as easy as Somerset had done in a stand of 181 for the first wicket.
Then Arul Suppiah made a double breakthrough to put Somerset back in command.
Adams had made 73 when he nudged Suppiah to Alex Barrow at short leg, and in the same over Rose Bowl newcomer Johann Myburgh was leg before without scoring four balls later.
Dawson reached the second century of his career off 183 balls but lost experienced Neil McKenzie to the penultimate ball of the day.
McKenzie had scored 20 when he edged Barrow to Trescothick at slip off what proved to be the last ball of the day to leave Hampshire 212 for three and still 16 behind the visitors.