Glamorgan 114 for 2 (Ingram 63*, Carlson 42*) trail Leicestershire 251 (Handscomb 46, van der Gugten 4-45, Douthwaite 4-49) by 137 runs
Timm van der Gugten was the pick of the Glamorgan bowling, grabbing the first four Leicestershire wickets to fall, while Dan Douthwaite also chipped in with four wickets to justify the decision to bowl first.
Leicestershire fast bowler Chris Wright made his first-class return from a drugs ban to help his side to a batting bonus point, his side recovering to 251 all out on a hybrid pitch in Cardiff.
Wright, who was banned for nine months but found not to be at fault after a banned substance was contained in a fruit supplement, combined with debutant Sam Wood and Tom Scriven as the last two wickets added 75 runs.
Glamorgan lost both openers early in reply, but moved onto 114 for 2 at the close with Colin Ingram, 63 not out, and Kiran Carlson, 42 not out, putting on an unbroken partnership of 87 to put their side in the driving seat.
After winning the toss and inserting Leicestershire in overcast and drizzly conditions, Glamorgan would have been hoping for an early breakthrough, which was delivered from a familiar source.
Van der Gugten has been the spearhead of the Glamorgan attack this season and he delivered once again, taking all three wickets to fall before the lunch break with arrow-like accuracy.
He bowled opener Rishi Patel for 7 with a delivery which clipped the top of off stump, then fellow opener Ian Holland played on with one which jagged back slightly when on 13.
The Dutchman returned to have a spell just before lunch and added a third, this time LBW as captain Lewis Hill did not get far enough forward to depart for 25.
Ned Leonard, on loan from Somerset, should have had a wicket when Indian star Ajinkya Rahane top-edged a pull shot, but deep midwicket Douthwaite was slow coming forward and ended up spilling the low chance.
It was the ever-reliable van der Gugten who brought the downfall of Rahane, finding the outside edge after lunch and helped by a sharp catch at second slip by captain Sam Northeast.
After looking good, England all-rounder Rehan Ahmed gave things away when he lifted a short ball from Douthwaite straight to Billy Root on the deep square leg boundary.
Then out of the blue Australian Peter Handscomb went for 46, trying to dab Douthwaite down to third man but instead just feathering a catch to wicketkeeper Chris Cooke.
Then New Zealander Fraser Sheat got into the act with his first wicket in county cricket, a rather tame dismissal of Liam Trevaskis who chipped the ball to mid-on.
The tame-ness was copied by Louis Kimber who also chipped the ball in the air, aiming a leg side half volley at catcher Asa Tribe off the bowling of Douthwaite.
That brought Sam Wood to make his debut in confident style as he and Scriven put on a half-century partnership, Wright and Wood doing the rest to reach the first batting bonus point.
Glamorgan's innings could not have got off to a worse start, captain Sam Northeast promoting himself to open and then departing first ball of the innings, caught behind by Handscomb from the bowling of Holland.
The same bowler accounted for debutant Asa Tribe, who played on for 4. Ingram and Carlson saw out the rest of the day's play to put Glamorgan in a strong position.
