Hampshire recovered from a poor start to finish on 261-6 against Glamorgan, who claimed two late wickets through Australian pace bowler Michael Hogan.
Hogan dismissed Sean Ervine and nightwatchman Danny Briggs after Hampshire had threatened to finish the day on top.
Former Western Australian Hogan finished the day with creditable figures of 4-66 and his victims also included the day's top scorer, the in-form Michael Carberry.
After the first hour had been lost to rain, Glamorgan captain Mark Wallace gambled on fielding first and with the wicket as troublesome early on as it often is, Hampshire were reduced to 4-2.
The lively Hogan broke through at the end of the third over when Hampshire captain Jimmy Adams, struggling for runs lately, edged to Wallace behind the stumps for a single.
Next man Liam Dawson made the same before being trapped by John Glover in the sixth but Glamorgan's successes then became much rarer as the wicket eased.
England candidate Carberry, particularly powerful in the Twenty20 competition but with a Championship century in his last match against Kent, fell six short of another.
This was after he and Neil McKenzie had taken the game away from Glamorgan a little in a stand of 130 for the third wicket in 45 overs, each batsman taking advantage of Hogan's rest periods by punishing those that followed him.
Left-arm spinner Dean Cosker removed McKenzie to a catch at the wicket at 134 before Hogan returned to the attack to have Carberry edging behind in sight of his 29th first-class century.
Carberry hit 16 fours and always looked in control after a circumspect start but his departure only heralded another major partnership.
James Vince and Ervine added another 90 in 20 overs for the fifth wicket, taking the score to 246.
Ervine, as belligerent as ever, hit Hogan for three fours in an over but at the start of the next, Hogan got his revenge thanks to a slip catch by Marcus North.
Briggs followed at 260 to Wallace's fourth catch of the day but Vince was in imperious form, reaching his half-century just before the close, ending 51 not out from 98 balls.