The 37-year-old Irishman made 106 to take his aggregate for the season to 838 as his side reached 227 for 3 in response to Glamorgan’s 335 for 9 at stumps on the second day.
A slow pitch was ideal for someone with Joyce’s phlegmatic temperament. He seldom played a cross-batted shot and it was a surprise when he chopped on to Tim van der Gugten in the 60th over.
Joyce survived one moment of alarm on 61 when Will Bragg put down a very difficult chance at slip off the debutant slow left-armer Owen Morgan, but Joyce’s ability to play straight and late once again paid dividends. He hit 14 fours in 177 balls faced.
Joyce had shared an opening stand of 133 with Chris Nash although Nash struggled for timing. Normally a fast scorer, it took him 66 balls to lodge his first boundary but he appeared to be finding some fluency when he shaped to cut Morgan and was caught behind for 37.
It was a deserved reward for the 22-year-old slow left-armer from Swansea who bowled with impressive control on his Championship debut. His efforts epitomised a persevering Glamorgan attack without their main strike bowler Mick Hogan who did not return after he ducked into a bouncer from Stuart Whittingham earlier in the day and was hit on the helmet.
Hogan spent ten minutes regaining his composure but eventually decided he could no longer continue. His condition will be monitored overnight but he is expected to be able to bowl on Monday.
With skipper Jacques Rudolph nursing a hand injury which will require an x-ray Glamorgan employed three substitute fielders including bowling coach David Harrison and Australian fast bowler Shaun Tait who has linked up with the squad as he prepares to play in their T20 side.
Sussex were 176 for 2 when Joyce was out and had added just five runs when Ross Taylor (4) was leg before playing across the line to Graham Wagg. But Luke Wells (41) and skipper Luke Wright (17), who is playing his first Championship innings of the season at Hove, added an unbeaten 46 for the fourth wicket.
Hogan’s retirement came after Glamorgan had added 44 runs to their overnight 291 for 7 during the morning. Both wickets fell to the impressive Whittingham who bowled with good pace in a spell of 8.1 overs which cost just 20 runs as he finished with a Championship best 4 for 58.
Thomas (15) was caught behind by a ball which seamed away before Rudolph, struggling after Whittingham struck him on the left hand, was caught at third man for 87 from 197 balls which was compiled in four and a half hours.
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