At 96 for five, 316 all out looked a distinctly long way away.
But Sean Ervine’s scintillating century and a brilliant late cameo from David Balcombe changed the mood.
An apparent bad day at the office for Hampshire suddenly became the kind of session that can transform a match and inject momentum into an entire season.
It was one of the greenest pitches seen in recent times at the Ageas Bowl.
This being the home side’s latest answer in attempting to solve the riddle of their near two-year winless home run in Championship cricket.
They have failed to win on home turf since July 2010.
But it was no huge surprise that Glamorgan opted to bowl on a pitch that had the seamers licking their lips after winning the toss.
At 22 for two early in the piece, it looked a good call.
Liam Dawson (six) and Michael Carberry (nought) departed, only for Jimmy Adams (42) and Simon Katich (36) to build a solid recovery, the latter falling shortly before the lunch break.
Soon after lunch, however, Adams and James Vince (nine) fell to leave the hosts in real trouble, until Ervine strolled out.
The Zimbabwean was the scourge of the Welsh club last month when he led Hampshire to a thrilling victory with a fine 75 at Cardiff.
No doubt they are sick of the sight of him by now.
He did it again with a 149-ball knock including 11 fours and one six – smashed over mid-wicket to bring up his century in real style.
With Michael Bates (41) leading the charge from the other end, Ervine eased himself into his innings.
He then cut loose to fire an unbeaten 109 that was sensible and aggressive in equal measure, steering the side to batting points they simply had no right to expect.
When Bates was bowled to leave the score at 159 for six, Hampshire were in trouble.
But Chris Wood (19), James Tomlinson’s lengthy stay for just four and Balcombe’s counter-attacking 39 saw the 300 barrier surpassed.
Ervine farmed the strike for the first phase of an 86-ball partnership that yielded 85 runs for the final wicket.
Balcombe was later trusted with full responsibility and rattled his career-best Championship score, with eight fours in his 42-ball knock.
But Ervine deserved his fine ovation for a sublime innings that could yet be pivotal as Hampshire search for that elusive home victory, with Glamorgan reaching 13 without loss at stumps on day one.