Hamish Marshall's innings of 114 enabled Gloucestershire to recover from a shaky start and finish on top at the Ageas Bowl, where Hampshire failed to make the best of helpful bowling conditions.
Gloucestershire were 56 for three in this LV= County Championship Division Two contest but recovered thanks to Marshall's diligence to finish on a respectable 349 for seven from 96 overs.
With the entire first day lost to rain it was a good toss to win on a green-looking wicket, under gloomy skies and amid blustery conditions. Hampshire's Jimmy Adams was the beneficiary and chose to field.
Immediately the home captain could see his decision justified as the man who called incorrectly, Gloucestershire's Michael Klinger, was out lbw to debutant Sohail Tanvir at the end of the first over.
Hampshire also brought in Dimitri Mascarenhas for his first championship match of the season and the wily veteran trapped Dan Housego in front for 10 and the score was 41 for two.
With the ball moving off the seam, batting was a hazardous business and Alex Gidman was next to go at, edging David Balcombe to Liam Dawson at second slip. Earlier, Dawson grassed a similar chance.
Then, as the sun came out, Chris Dent was joined by Marshall, pictured, and the Gloucestershire recovery began.
The obdurate Dent batted through the difficult first session for 34 but added only one more after the lunch break before providing Sohail with his second and last wicket of the day, Dawson again holding on in the cordon.
Marshall, now 34 and seven years on from the last of his 13 New Zealand Test caps, lifted Balcombe for the first of his two sixes as Hampshire felt their morning advantage slipping.
Benny Howell offering solid support. The fifth wicket was worth 106 in 28 overs before Howell was bowled by Sean Ervine for 54 - an innings which included eight boundaries against his old club.
Marshall hit the spin of Dawson for his other six on his way to the 22nd century of his first class career, before Balcombe found an edge at 289 and Dawson completed his third catch.
Marshall faced 184 balls and also hit 13 fours and by the time of his departure Gloucestershire had gained the upper hand.
In the evening session, Gloucestershire also lost Will Gidman at 338 to a catch behind off Mascarenhas but Gareth Roderick and James Fuller saw their side through to the close without further mishap.
Sohail can be satisfied with his first appearance, finishing with 2-68 runs off 20 overs, while there were two wickets apiece for Balcombe and Mascarenhas.