Reece made 111 and Alex Hughes an unbeaten 63 to take Derbyshire to 253 for 5 before a combination of bad light and rain ended play early.
It was a mixed day for Glamorgan who summoned Andrew Salter from Wales in the morning to replace Kieran Bull after he was ruled out with a back spasm, although Michael Hogan impressed with figures of 2 for 45 from 16 overs.
Billy Godleman’s decision to bat on a cloudy day might have backfired had Glamorgan been able to find a consistent line and length after an excellent opening spell from Hogan.
The fast bowler beat the bat several times before a full-length ball trapped Godleman on the crease in the ninth over but Glamorgan’s inability to apply any sustained pressure allowed Reece and Wayne Madsen to rebuild the innings.
Daniel Douthwaite, straining to impress on his championship debut, leaked 31 runs from four overs, and it was only when Hogan returned that Glamorgan were able to exert some control.
He tempted Madsen in his 150th first-class match for Derbyshire into a loose drive at the final ball of the morning and Glamorgan were rewarded for a more disciplined approach when Tom Lace edged Lukas Carey to third slip.
But Reece and Hughes showed judgement and patience to regain the initiative, helped by a couple of wayward overs from David Lloyd and Hogan with Reece completing his first red ball hundred since April 2018 from 159 balls.
It was a timely return to form for the opener whose previous four championship innings this season had yielded only 49 runs but his departure shortly before tea saw another shift in the balance of the day.
Douthwaite tempted him into a top-edged pull that was taken at fine leg and Glamorgan had another success to celebrate in the penultimate over of the session.
The fourth wicket stand with Hughes had put on 104 in 22 overs but only four more runs were added before Marnus Labuschagne yorked Harvey Hossain with the last ball of his first over.
The Australian all-rounder almost bowled Matt Critchley who was also surprised by a bouncer from the leg-spinner but when the weather closed in , Derbyshire had secured a second batting point with Hughes following his unbeaten century in the previous four day game at Bristol by completing 3,000 first-class runs for the county.