Glamorgan 123 and 499 for 5 (Carlson 187*, Labuschagne 138) lead Sussex 481 (Coles 138, Smith 89, Haines 58) by 141 runs

Paul Farbrace, Sussex’s head coach, revealed afterwards that Robinson had been suffering from a sore left ankle, and will be sent for a scan on Monday to determine the extent of the injury. With England’s first Test of the summer against Ireland starting in 12 days’ time, and James Anderson already nursing a “minor groin strain” less than a month out from the Ashes, the news of Robinson’s discomfort will be of concern to Ben Stokes, the Test captain, who had previously stated his desire to have eight fit seamers to take on Australia.

“He’s got a sore ankle and he’ll be scanned on Monday to see how bad it is,” Farbrace said. “We knew it was sore yesterday and that’s why we got one spell out of him this morning. Once he was off that was it for the day.

“It was precautionary, there was no point in making it worse. We knew that he was sore. It’s walking more than anything, it’s not actually the running part that makes him sore. It’s a joint decision between our medical team and the England medical team, we’ve got a good relationship. It’s the right thing to do, we need to find out and Oliver wants to find out what’s going on with the ankle and why it’s so sore.”

Robinson, who required a cortisone injection in his back before his first appearance of the season, has had his workload carefully managed by the ECB. He has featured in three of Sussex’s six games so far, taking career-best match figures of 14 for 117 against Worcestershire two weeks ago.

He began this match with 4 for 29, including the wicket of Labuschagne for 1, as Glamorgan were dismantled in their first innings but on Saturday, after completing an eight-over spell during which he saw Carson dropped, he walked from the field and did not return. On the Sussex YouTube channel, there remained a poll asking how many wickets Robinson would take in the day, with four options: 2, 3, 4 or 5+.

Where there was far greater certainty was in the identity of Glamorgan’s saviours. Carlson, stand-in captain for this match in the absence of the hamstrung David Lloyd, produced a mighty, unbeaten 187 and Labuschagne did Labuschagne things to steer their side away from the jaws of a three-day defeat. At the close, Glamorgan’s lead was 141 with five wickets standing: pushing for a first victory at Hove since 1975 will be a stretch but two more sessions of batting on a pitch that has appeared increasingly moribund would almost certainly secure an unlikely draw.

Glamorgan had begun the day 240 runs in arrears with nine wickets standing, and the loss of two in the space of two balls inside the first half an hour suggested they were facing an uphill task. Perhaps, if James Coles had held a low catch at third slip when Carson was on 3, events would have taken a markedly different course. Glamorgan would have been 136 for 4, Robinson would have had a wicket midway through his spell, and Sussex might have been sufficiently buoyed to keep chipping away and then roll through with the second new ball during the afternoon.

Carlson gave a much harder chance when he had made 21, advancing to sting the fingertips of Jack Carson with a lofted drive that flew for four, but was more or less impregnable thereafter as he and Labuschagne spent the afternoon assembling a stand of Brobdingnagian proportions – on the way scrubbing the contributions of Viv Richards and Tony Cottey from the records books, for Glamorgan’s highest fourth-wicket stand against Sussex.

After a watchful start, which involved seeing off Robinson, the pair set about transferring the pressure back on to the Sussex attack. Carlson was the more fluent, reaching his fifty with a reverse-sweep from 78 deliveries, and then requiring only 49 more to get to his third century of the summer, secured by a tuck into the leg side for three off Tom Haines. His was the more exuberant celebration, too, the bat whirled like a scimitar before the helmet was removed to reveal a satisfied grin beneath Carlson’s bristling moustache.

Labuschagne, quite clearly, was not bothered about being outscored and seemed to have only two things on his mind: salvage the match situation for Glamorgan and face as many balls as possible in his final innings before joining up with Australia for their World Test Championship and Ashes campaign.

He was struck a blow on the bottom hand by Karvelas, shortly after clubbing Carson into the Cow Corner hospitality section, but shook it off after a brief visit from the physio, and brought up his own fifty off 121 balls with another swipe for six, this time off Coles. The closest he gave to a chance during an innings that spanned more than five hours was when edging Carson wide of the diving Steven Smith when on 73, as Labuschagne also upped the tempo to bring up his hundred from 185 balls with back-to-back boundaries off Fynn Hudson-Prentice.

Almost every noteworthy contribution from Labuschagne was met with increasingly raucous chants of “Oh Glammy, Glammy!” – possibly with an Aussie twang – from a knot of supporters in the Sharks Stand. By the time he missed one that skidded on straight from Coles to be lbw for 138 from 244 balls, the Marnus Fan Club were waving their shirts around their heads as their hero walked back to applause from all four corners of the ground.

Expectations for the day had been completely reversed by that stage. Carson struck in his fourth over of the morning, Zain-ul-Hassain’s second tidy innings on debut ending when he dragged his back foot out of the crease attempting to sweep. Sam Northeast came and went like Abe Simpson at the Maison Derrière, trapped by one turning into him, but that was Sussex’s last success for more almost 65 footslogging overs as Labuschagne and Carlson turned the screw. Coles’ two wickets in the final session kept Sussex interested – in absolute terms – but Glamorgan will return in the morning looking to complete their great escape.