Keaton Jennings overcame his disappointment at not being selected for England's Test tour to India by starting his Vitality County Championship campaign with a half-century.
Jennings, who opened the batting, impressed as part of the England Lions squad supporting the Test squad in the sub-continent this winter. He was not chosen for the main event, with Ben Duckett and Zak Crawley remaining Ben Stokes' and Brendon McCullum's preferred opening pair.
Jennings scored 85 runs with only one dropped catch in an authoritative innings, while his opening partner Luke Wells reached 55.
Lancashire finished the day on 233 for four, 134 runs behind Hampshire's first innings total on a placid Utilita Bowl pitch.
In good batting conditions, Wells and Jennings took advantage after bowling the hosts out for what felt like an about-par 367.
The battle between Mohammad Abbas and Wells was intriguing. Abbas sent down 16 challenging dot-balls before Wells could manoeuvre himself off strike.
From that point, the former Sussex opener slowly worked his way to the top of the home side's bowling attack, on his way to his first half-century of the season.
He found straight driving particularly profitable, reaching the milestone in just 65 balls - the 68th fifty of his career.
Wells was dismissed to end an 87-run partnership. He had scored 55 runs before clipping Abbas to Tom Prest at short midwicket. This made him the fifth batter to reach 50 runs but not 100.
Jennings had a less aggressive approach but never appeared to be in much danger as the Kookaburra ball quickly lost its hardness.
To counter the slow pitch, he adopted the strategy of batting further out of his crease. Lancashire's approach was to hit down the ground, while Hampshire dominated the square.
Jennings was dropped at the point on 36 by Nick Gubbins, who lost his trousers in the process. He then went on to score his 57th first-class half-century, taking 122 balls to reach the milestone.
Josh Bohannon scored 30 runs out of 38 before being dismissed by James Fuller, who was under pressure from the Pavilion End, after a build-up by Kyle Abbott and Fuller.
Jennings then partnered with George Balderson in an 86-run stand that seemed endless until Balderson carelessly slogged to deep midwicket for 38. Tom Bruce was then caught brilliantly at first slip by Liam Dawson, giving Holland two wickets in two balls and turning the momentum.
George Bell narrowly avoided edging the hat-trick ball before surviving until the close with Jennings.
Earlier, Hampshire added 62 runs to their overnight score, extending their first innings by an hour and a half and earning three batting points.
Dawson had ended the previous day on 61, continuing his good form from the previous season. He continued to score steadily with Ian Holland and James Fuller in partnerships of 38 and 45 runs respectively.
Apart from a brief acceleration to reach 350 with plenty of time remaining, during which Dawson hit Will Williams for six, there was little variation from a slow pace.
Holland was dismissed leg before wicket by Williams, while Fuller edged a drive off Wells to a helmeted Jennings at first slip. Dawson was caught behind by Tom Bailey for an innings-high 86. As a result, none of Hampshire's four batsmen who scored fifty were able to reach a century.
Nathan Lyon finished the innings with figures of three for 110 from 38.1 overs after Kyle Abbott was caught at long-on by Jennings.
Lancashire then settled in and took advantage of the pitch and ball, which were conducive to patient long-form batting.