Glamorgan 139 and 232 for 5 (Ingram 102) need a further 100 to beat Worcestershire 271 and 199 (Neser 4-50)
Ingram has seized the opportunity to fill the gap left by Australian star Marnus Labuschagne and been making the most of his return to red-ball cricket.
He had played only game in that format in four years before this season but has responded with 83 versus Durham and 178 against Sussex in his previous two Championship appearances.
Ingram was finally dismissed shortly before the close for 102 and the second new ball will be available first thing on Wednesday morning with 100 required by the visitors.
Glamorgan captured the final four wickets for 52 runs in 13.4 overs after Worcestershire resumed on 147 for 6. Pace bowler Michael Neser picked up two more wickets to finish with match figures of 7 for 90 and take his tally for the campaign to 32.
Neser has been the most impressive bowler on either side in this game, exploiting a pitch on which the occasional delivery has taken off.
Only Middlesex’s Toby Roland-Jones and Durham’s England pace bowler Matt Potts have taken more Division Two wickets this summer than the 32-year-old.
Gareth Roderick fell victim to a lifter from Neser as an edge flew to to Ingram at third slip. Glamorgan keeper Tom Cullen snaffled his eighth catch of the game after Joe Leach aimed an expansive drive at Michael Hogan.
Josh Baker cover drove Hogan for four to extend the lead past 300 and he and nightwatchman Charlie Morris added 33 for the ninth wicket. But spinner Andrew Salter ended the innings with two wickets in two balls as he bowled Morris, on 29, and held onto a return catch from Dillon Pennington to leave Baker undefeated on 25.
When Glamorgan batted, opener David Lloyd had a let off before he had scored off Leach, with Baker failing to hold onto a head high chance at fourth slip. But it was not a costly miss for the home side with Lloyd making just 13 before driving Morris straight to mid-off.
The second-wicket pair of Edward Byrom and Colin Ingram were relatively untroubled and the former hooked Pennington for six. Their partnership was worth 57 but then Byrom attempted a reverse sweep against Baker and the ball lobbed up to slip.
Sam Northeast was also guilty of giving his wicket away when he slashed at a widish delivery from Morris and picked out Pennington at third man.
Ingram on 53 survived a hard chance to Tom Fell at second slip off Ed Barnard and completed a 103-ball half-century.
There was little Kiran Carlson could do to avoid a delivery which climbed on him from Pennington as Roderick took the catch. But then Billy Root joined forces with Ingram to add 95.
Ingram swept Baker for four to reach three figures but then was undone by a Barnard delivery which nipped back and was lbw. His 203-ball knock contained 13 boundaries.