The Sussex skipper made 101 in a total of 229 all out with Chris Nash (40) the only other batsman to make a significant contribution after Middlesex had won the toss and elected to bowl first.
It continued Joyce’s excellent form this season having made an unbeaten 204 in his previous Championship match at Nottinghamshire and was arguably a better innings on what was a lively wicket.
Sussex will have been disappointed not to make a few more runs with a number of batsmen guilty of getting out to careless shots and Middlesex built on their advantage by reaching 44-0 at the close.
Sussex got off to a solid start after being put into bat but lost three wickets in quick succession before lunch to hand Middlesex the initiative.
Luke Wells became Gurjit Sanhu’s maiden Championship wicket when he edged behind having made 15 with Mike Yardy falling for a golden duck to Gareth Berg to leave Sussex on 49-2.
Chris Nash played nicely for his 40 from 63 balls but his luck ran out when a thick edge flew to Sam Robson at gully to give Berg his second wicket.
Rory Hamilton-Brown put on 41 with Joyce before offering no shot to Neil Dexter’s second ball and seeing his off stump knocked out of the ground.
Joyce continued to tick along serenely as he reached his fifth first class 50 of the season off 85 balls, including nine fours.
Nobody was able to stay with the Sussex skipper for too long though with Luke Wright slapping a catch straight to short midwicket off Ollie Rayner having made 22 in a partnership of 56.
Ben Brown and Chris Jordan all went cheaply while Steve Magoffin became the second gold duck of the innings as Tim Murtagh picked up two wickets in two balls to leave Sussex on 196-8.
Joyce had little option but to go on the offensive as he ran out of partners and brought up his century in style by uppercutting Berh for six.
He fell shortly afterwards when he played on trying to cut a ball from Dexter having made 101 from 166 balls.
Berg went on to remove Anyon to finish with figures of 3-49 as Sussex were dismissed for 229.
That left Middlesex with 13 overs to bat before they close and Dawid Malan (27) and Sam Robson (11) survived a couple of scares to finish on 44-0.
A number of edges flew through the slip region while Wright was unable to hold on to a difficult one-handed catch at mid-off when Robson drove Magoffin in the air.