James Hamblin tormented Sussex's Second XI with his second century of the match as Hampshire looked to set a testing victory target in the championship battle at Hove.
Hamblin hammered 124, one more than his first innings score, to help guide his side to 263-8 and an overall lead of 289 going into the final day.
Sussex earlier batted on for 70 minutes, adding 93, before declaring on completion of a fourth batting point having reached 352-7.
Hamblin, who played for Sussex Seconds before making the move to Hampshire two years ago, frustrated the hosts by producing a four-and-a-half hour vigil which included 18 boundaries.
The 24-year-old from Kent had faced 168 balls when he got out to a tired shot off Mike Yardy, top-edging an attempted aim to mid-wicket and falling to a catch at deep backward point by Krishna Singh.
Hamblin revived his side after Paul Hutchison had them in early difficulty with the wickets of Lawrence Prittipaul (3) and Will Kendall (20).
Hutchison removed Prittipaul for the second time in the match by having him caught at gully and then trapped Kendall leg before.
But Hamblin then added 76 for the third wicket with Chris Benham (30) before Greg Lamb (39) joined him to add 95.
Off spinner Chris Nash, who bowled only five overs with the wicket not appearing to take spin, bowled Nash and Billy Taylor later pinned Lamb leg before.
Taylor, who finished the day with 4-57 from 26 overs, also struck to have Kevin Latouf caught at slip for a first ball duck and Iain Brunnschweiler leg before for 3.
Hamblin was eventually seventh out at 237, and James Hibbert (21) and Charlie Van Der Gucht (4) were together at the close with Hampshire aiming to push their lead over 300.
Teenager Andrew Hodd earlier finished unbeaten on 43 and Hutchison made 29 not out as Sussex pushed on after resuming on 259-6. Nash was the only additional wicket to fall being bowled by Lamb, who ended with 2-47 in 19 overs.
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