Stand-in skipper Hamish Marshall led from the front with his second century of the season as Gloucestershire reached 308-5 on the opening day against Glamorgan at Bristol.
Having won an important toss, the experienced former New Zealand Test batsman, leading his side in the absence of Michael Klinger, made 109, hitting a six over long-on off Andrew Salter and seven fours.
Despite the best efforts of Michael Hogan, who bowled with great heart on an unhelpful pitch to claim three for 39 from 19 overs, Glamorgan were unable to prevent their hosts taking a grip on the game.
Will Tavare hit a solid 77, Ian Cockbain 51 and Alex Gidman 26 in a determined Gloucestershire batting effort.
The hosts had to rule out Klinger before the start with a foot injury, sustained in the previous evening's NatWest T20 Blast game against Hampshire, and then lost wicketkeeper Cameron Herring to a damaged finger sustained in the warm-up.
Seventeen-year-old Academy keeper Patrick Grieshaber, a Jack Russell discovery, from Marshfield, near Bath, had to be summoned from local club cricket and registered with the ECB to play for the first XI in order to make his debut.
It was as well Marshall won the toss and elected to bat, giving Grieshaber, a product of Gloucestershire's schoolboy set-up, time to reach the ground before he was required.
The home side needed a calming influence after the injury setbacks and the early loss of opener Chris Dent, who departed for two to a catch at square-leg off Hogan.
They found it in the unflappable Tavare, who is making a big impression in his debut season. The nephew of former England batsman Chris Tavare already has two hundreds to his name and added a half-century off 87 balls, with 10 fours.
Alex Gidman survived a big appeal for a bat-pad catch at short-leg off Dean Cosker before having his stumps scattered playing across a ball from Ruaidhri Smith and falling with the total on 83.
Lunch was taken at 98-2 and the early afternoon session produced the most compelling cricket as Hogan summoned up lively pace from the Ashley Down Road End. He gave Tavare and Marshall a torrid time before bowling Tavare between bat and pad.
The in-form seamer sent down eight hostile overs for 19 runs. But Marshall survived and went to his half-century off 94 balls, with four fours.
He and Cockbain continued to prosper in the final session after tea had been taken at 194-3.
Marshall opened his shoulders to dispatch Salter for six and four off successive deliveries, moving to a 164-ball ton, while his partner emerged from a scratchy start to reach a half-century off 131 balls before being pinned lbw by a ball that kept low from Jim Allenby.
They had added 145 to put Gloucestershire in control. Hogan then steamed in with the second new ball and bowled Marshall of an inside edge to claim his 100th first class wicket for Glamorgan in just 20 matches.