Glamorgan ended Day 1 at Colwyn Bay with a 172-run lead as Lancashire reached close of play on 85/1 in response to the home side's 257 all out in their Specsavers County Championship match.
Opener Charlie Hemphrey top scored with 56, seam bowler Lukas Carey smashed 51*, and new loan signing Samit Patel hit 54 on his Glamorgan debut to help marshal the tail to a second batting bonus point.
"I wasn't going to be taking part for Notts in Scarborough," said Patel. "Director of cricket Mick Newell said Glammy had come in for me to play four-day cricket, so I was thrilled to bits to do that.
"An opportunity in the Euro-league got cancelled. I can go back and play T20 for Notts but hopefully to get promotion for Glamorgan is on the agenda. I haven't really thought about next season.
"The wicket is a good one, we're probably a bit short with the bat, but we've got to keep grinding away."