Marnus Labuschagne and Kiran Carlson both hit centuries as Glamorgan rallied on day three at the 1st Central County Ground.
Starting the day 240 runs behind, the visitors needed a big total. On a flat Hove wicket, Carlson and Labuschagne were happy to oblige.
Joining forces half an hour into the morning session, the pair put on a mammoth 288-run partnership.
Dropped early in his innings, Carlson acted the aggressor, taking on Ollie Robinson with two forceful drives in the morning session. He soon passed fifty and turned his attention to Jack Carson. Dancing down the track, Glamorgan’s captain hit the off-spinner for a flurry of crisp boundaries.
Labuschagne got in on the act in the 54th over, cutting Carson for four before he too came down the pitch to smack an imposing six.
Despite taking two wickets in two balls – Zain Ul-Hassan stumped and Sam Northeast lbw, it was a long and unsuccessful day for Carson. Bowling throughout, the 23-year-old was plundered for 179 runs from his 39 overs.
Fynn Hudson-Prentice also took some tap, finishing with figures of 0-81 – Carlson punishing the all-rounder through the covers in the 67th over.
With his partner on the offensive, Labuschagne had licence to hang back. In a comparatively pedestrian knock, the Australian was happy to defend, leaving anything possibly dangerous and rotating strike when possible.
After a steady few overs, he claimed fifty on the stroke of lunch, cutting James Coles for consecutive fours to reach the milestone off 122 balls.
Both batters completed their tons in the afternoon session – Carlson with a wristy clip off Tom Haines, Labuschagne with a forceful pull-shot off Hudson-Prentice. Warm applause greeted both as Glamorgan assumed control – Sussex’s 358-run lead surpassed.
One notable absentee was Ollie Robinson. After a lengthy spell in the morning session, the England man didn’t take the field for the remainder of the day’s play.
There was no explanation – and three weeks from the first Ashes Test match, his absence will cause concern for England supporters.
So too will the form of Marnus Labuschagne, who finally fell for 138 runs off 244 balls – trapped lbw by James Coles. It was a majestic knock from a world class cricketer.
After leaking runs in the afternoon, Coles would also fox Billy Root, the diminutive batter caught by Alsop for 24.
The wickets failed to faze Kiran Carlson, however. After surpassing 150, he once again ran down the pitch to Carson, hitting his second six to accompany 18 fours.
The Welshman’s ruthless knock left him just 13 runs away from his maiden first-class double-century at stumps.
Going into the final day, Glamorgan are 499-5, leading Sussex by 141 runs – the game firmly in the balance.