Sussex had managed only one century partnership for the first wicket since June 1997, but Montgomerie and Peirce put on 136 to launch their new-look side towards their total of 285 for 5 in 96 overs.
After the Lancashire groundstaff had scraped ice from the covers to allow play to get under way half an hour late, Montgomerie, who moved to Sussex from Northamptonshire in the winter, justified the decision by his captain, Chris Adams, to bat by making 62 from 164 balls before edging Glen Chapple to Mark Chilton at second slip.
The left-handed Peirce went on to reach 77 from 204 balls, including eight fours, before being caught behind off Peter Martin.
Adams hit his third ball from Mike Watkinson for six to get off the mark but also fell caught behind, for 26, to give Lancashire's debutant seamer, Mike Smethurst, his first Championship wicket.
Tony Cottey fell for 46, on his debut after leaving Glamorgan, but Sussex will resume this morning well in charge.Reuse content