Glamorgan 81 for 4 (O'Neill 2-6) trail Nottinghamshire 279 (Haynes 100, O'Neill 59, van der Gugten 4-54, Hadley 4-76) by 198 runs
England opener Ben Duckett was out for just 25 on his return to Rothesay County Championship cricket but a century from former England Lions batter Jack Haynes helped champions Nottinghamshire overcome a shaky start to post 279 against promoted Glamorgan, who were 81 for 4 at the close.
Haynes made exactly 100, hitting a dozen fours, and shared an 111-run partnership with Australian seam bowler Fergus O'Neill as Nottinghamshire recovered from 103 for 6 on a pitch offering help to the Glamorgan bowlers, of whom Timm van der Gugten and Ryan Hadley picked up four wickets each.
O'Neill then struck twice in his opening spell and England's Josh Tongue chipped in with his first wicket of the season, before Glamorgan lost skipper Kiran Carlson two overs from the close.
Glamorgan deployed an injury replacement at the end of the Nottinghamshire first innings with Sean Dickson replacing Ben Kelleway, who reportedly sustained a hip flexor injury while fielding.
Nottinghamshire's troubles with the bat had started with the first ball of the day as captain Haseeb Hameed was bowled through the gate by a van der Gugten delivery that ducked in sharply to send leg stump flying. By the seventh over, the defending champions were 38 for 3 as Ben Slater nicked to third slip and Duckett was caught off a leading edge at mid-off, the chance well taken by Andy Gorvin, tumbling backwards.
Duckett, making only his second appearance for his county in 21 months with his England place under scrutiny after a poor Ashes series, was typically assertive but it was a pitch he would doubtless have preferred not to have to negotiate on the first morning.
Joe Clarke unfurled some classy shots, hitting six fours, but had no answer when Gorvin brought one back sharply to bowl him. With Kyle Verreynne caught at point as van der Gugten continued to thrive, Nottinghamshire were 95 for 5, which became 103 for 6 as the Netherlands international struck with his first ball of the afternoon, beating Liam Patterson-White's defence.
With a short boundary on the Bridgford Road side, the scoring rate was healthy, even as wickets fell. Nottinghamshire bat deep, with every chance that at least one passage of play would see them prosper. It came when Haynes and O'Neill added 111 in 21 overs for the seventh wicket.
Though recruited primarily for his qualities with ball in hand, O'Neill can bat, as he proved with his second first-class half-century in Nottinghamshire colours, his fifth overall, threatening more before Gorvin saw him off.
Haynes, meanwhile, advanced into the 90s, where the experience of making it to a hundred four times last season will have served his patience well as he endured a half-hour wait to complete the job.
He saw Brett Hutton and Tongue come and go as he waited for opportunities, limited to a diet of singles and grateful to last-man Dillon Pennington for keeping out seven balls before he was able to push Zain-ul-Hassan down the ground for the one that mattered, before being caught at long-off without further addition.
In the first appearance of his second spell at Trent Bridge, O'Neill wasted little time in successfully executing his primary skill, dismissing both Glamorgan openers in his first 14 balls without conceding a run. Asa Tribe was leg before, the ball striking him right on the line of off-stump, Eddie Byrom nicking to first slip.
Carlson joined Zain to weather the next 15 overs without mishap but with the light becoming gloomier, England pace bowler Tongue entered proceedings at the Stuart Broad End and needed only seven deliveries to dismiss Zain for 27.
With the experience of Colin Ingram for company, Carlson would have hoped to guide his side to the close without further loss, only for Verreynne, standing up to Hutton, to remove him with a sharp catch.
