Brett D'Oliveira and Joe Clarke both scored their second Specsavers County Championship centuries of the season to put Worcestershire in a strong position after day one of the clash with Glamorgan at the Swalec Stadium.
The pair featured in an unbroken third wicket stand of 209 in 49.2 overs as Worcestershire closed on 343-2 from 96 overs.
Worcestershire's record third wicket partnership in matches between the two counties is the 264 by Brett's father Damian and Graeme Hick at Abergavenny in 1990.
Brett D'Oliveira, who had scored his maiden Championship hundred against Essex at New Road on Tuesday, ended unbeaten on 152 from 299 balls with 23 fours.
It was scored exactly 51 years since his grandfather Basil registered his first Championship hundred for the County against Essex at New Road.
Brett, who survived two chances, showed immense powers of concentration in batting through the day.
He reached his 50 from 113 balls and his century was completed from 227 deliveries.
England Lions player Clarke followed up his ton against Gloucestershire at Bristol with 105 not out from 139 balls with one six and 14 boundaries.
The 19-year-old reached three figures in the penultimate over of the day.
It was third first-class century of the season – he launched the campaign with a ton aganst Oxford MCCU – although he was dropped from a caught and bowled chance on 83 by Graham Wagg.
Now Worcestershire will be keeping their fingers crossed that the rain forecast during the next two days does not materialise.
Worcestershire opted to bat after winning the toss and skipper Daryl Mitchell was trapped lbw by Craig Meschede for three at 26-1 in the seventh over.
Moeen Ali survived a caught and bowled chance on five against Michael Hogan with 42 on the board.
D'Oliveira immediately looked in good form and scored 33 of the first 50 runs which came up in the 20th over.
The second wicket pair were given a searching examination by the home side's pace attack during the morning session.
But Moeen produced one of the shots of the morning, a straight drive for four off Timm van der Gugten.
By lunch D'Oliveira had moved onto 41 from 88 balls and Moeen 22 off 75 deliveries with the 50 stand coming up in 23 overs.
The second wicket partnership was extended to 108 in 40 overs before Moeen was caught behind by keeper Mark Wallace for 55 at 134-2 in the 47th over.
The England all-rounder struck 10 fours in his 125 ball knock.
That was Glamorgan's last success as D'Oliveira and Clarke dominated the remainder of the day.
Worcestershire gave a debut to New Zealand all-rounder Mitchell Santner in place of paceman and fellow Black Cap Matt Henry.
Santner was one of three specialist spinners in the Worcestershire side along with Moeen and D'Oliveira while Glamorgan included none in their line-up.
Glamorgan made three changes to their line-up from the side which lost to Kent by ten wickets at Canterbury with Mark Wallace, Nick Selman and Timm van der Gugten returning to the line-up in place of James Kettleborough, Andrew Salter and Harry Podmore.