The opening batsman has grabbed 30 in 14 appearances, 10 more than Worcestershire’s Daryl Mitchell.
Lyth took seven catches in Yorkshire’s previous Championship game against Middlesex at Scarborough last month, and he took another two yesterday as Sussex scored 315-8 after being sent into bat.
But it was a chance that Lyth did not grasp – a chance he would normally have grabbed 99 times out of 100 – that defined the course of the opening day.
The total was 55-2 when Jack Brooks, bowling from the Peasholm Park end, found the outside edge of Craig Cachopa’s bat.
The ball flew to second slip, where Lyth dropped a simple one by his standards, wicketkeeper Jonny Bairstow just failing to snaffle the rebound.
In those frantic seconds, a great roar went up from a crowd of 4,624 followed by a great groan of disappointment.
What should have been 55-3 had instead become 169-3 by the time Tim Bresnan ended a stand of 124 in 44 overs between Cachopa and Ed Joyce, a stand that tipped things Sussex’s way.
Cachopa, a South African-born former New Zealand U-19 captain with a Portuguese passport (work that one out), had five runs at the time and went on to 53, made from 134 balls with seven fours.
Diminutive and determined, he was the perfect foil for Joyce’s more expansive method, which frustrated Yorkshire for almost six hours.
On a sunny day blown by a freshening wind, Joyce, the Sussex captain, top-scored with 130 from 240 balls with 15 fours.
With Luke Wright chipping in with 52 from 74 deliveries, it was a difficult day for the Yorkshire bowlers, who would have expected richer reward.
Collectively, though, they did not quite justify the faith shown in them by Andrew Gale, the Yorkshire captain, who was attracted by moisture in the North Marine Road surface.
Although not obviously a bowl-first day, the pitch here often flattens out and 55-3 would have represented a return that more than justified that choice.
Yorkshire were initially much too short as Sussex raced to 44-0 inside nine overs, Chris Nash pulling powerfully and cutting confidently.
Nash hit seven boundaries in a run-a-ball 35 that was a bit like your average English summer – good while it lasted, but over in a hurry.
Nash, the 31-year-old right-hander, fell to the penultimate delivery of that ninth over when Lyth took a splendid catch moving to his left in front of first slip Alex Lees after Ryan Sidebottom located the edge.
It showed what could be achieved when the ball was pitched up, and Sidebottom struck again with the second delivery of his next over when Luke Wells, playing defensively off the back foot, edged into his stumps.
Sidebottom had captured 7-44 – the second-best figures of his career – in Yorkshire’s previous County Championship match here. He was not quite at his sparkling best yesterday, but the left-armer still stood out along with the excellent Steve Patterson.
Yorkshire, who went into the game five points clear at the top, struggled to build pressure after Sidebottom’s double strike as the visitors lunched on 99-2.
They got their act together more in the first period after the break, when Patterson locked into a nagging length, but Joyce and Cachopa displayed the virtues of patience and perseverance.
Just when it seemed they might never be parted, Cachopa rather gave it away when he tried to steer Bresnan through third-man but succeeded only in picking out Lyth, who took a good high catch at second slip.
Moments earlier, Kane Williamson had dropped a tough half-chance, diving full length to his left at third slip, that would have removed Joyce on 60, also off Bresnan, in the only life the left-hander enjoyed.
At tea, Sussex were very well placed at 206-3, but Yorkshire stuck to their task in the final session.
Wright, one ball after reaching his half-century, got an inside-edge into his stumps off Patterson to end a stand of 68 in 21 overs with Joyce, who went to his hundred from 202 balls with 12 fours when he tickled Adil Rashid for two to fine-leg.
Brooks found late reward when he struck in the second over with the second new ball, pinning Steffan Piolet to leave Sussex 260-5.
It was a significant wicket for the 30-year-old, his 50th in the Championship this year, and No 51 followed when Ben Brown was caught at third slip by Williamson, drawing Brooks level with Sussex’s Steve Magoffin and one behind Lancashire’s Tom Smith at the top of the First Division’s wicket-takers’ list.
In the closing stages, James Tredwell edged Patterson to Williamson at third slip and Joyce fell lbw trying to pull Rashid.