Murray Goodwin led the way with his 70th first-class century as Glamorgan's top order made promotion-chasing Lancashire toil on the opening day of their LV= County Championship Division Two match at Emirates Old Trafford.
After opting to bat, Glamorgan made hay in the Manchester sun when reaching 315 for three off 97 overs.
Former Zimbabwe international Goodwin, 40, ended the day unbeaten on 138 having shared in an unbroken 130-run stand with Jim Allenby, who struck 68 not out.
Earlier, Glamorgan opener Gareth Rees made 58 as in-form Lancashire, who have a one-point lead over second-placed Northamptonshire having played a game less, struggled to make any impression on a pitch that is good for batting and expected to offer significant turn later on.
Will Bragg was the first batsman to go in the 17th over when he drove at Simon Kerrigan and was caught at slip by Ashwell Prince, leaving the score 43 for one.
Lancashire had to wait until after lunch for their second wicket, Rees superbly taken at first slip by a diving Andrea Agathangelou off Kyle Hogg as he drove.
The third wicket was that of debutant Chris Cooke, who was culpable as he slapped a short ball from Kerrigan straight down Luke Procter's throat at cover just before tea.
Goodwin's fourth championship hundred of the campaign arrived in his 20th match against Lancashire for either Glamorgan or Sussex.
He shared in partnerships of 77 inside 21 overs for the second wicket with Rees, 65 in 25 for the third with Cooke before uniting for 35.3 with Allenby.
The Zimbabwean offered Kerrigan a return catch while on 129 late in the day, yet it was not taken.