Adam Lyth scored a battling century as Yorkshire secured a first-innings lead of 150 over Lancashire on day two and pushed hard for victory at Headingley.
Yorkshire, replying to 123, started the day at 93 for two and, as the description of Lyth’s innings suggests, had to work hard for their runs against an improving visiting attack, who restricted them to 273 all out on the stroke of tea.
Lyth notched his first four-day hundred of the season and the 22nd of his first-class career, including 17 of them in the Specsavers County Championship.
He reached three figures after lunch off 233 balls having spent 71 minutes in the nineties and later saw Lancashire reach close on 141 for four from 48 overs, a deficit of nine.
Speaking at the close of play, 29-year-old Lyth said: "I'm very pleased with how it's gone for me in this game. I've had a tricky few games opening the batting, but I'm really pleased to get a hundred in a Roses match and hopefully in a match-winning performance as well."
Clark and England Lions seamer Saqib Mahmood equally shared six wickets for a Red Rose side who benefited from an increased consistency with the ball today.
They also caught well, highlighted by a one-handed stunner from Ryan McLaren at second slip off the slippery Mahmood to get rid of Jack Leaning shortly before lunch.
Leaning and Lyth had shared 64 for the fourth wicket to advance the score from 120 for three.
It was the first of two wickets in two balls for Mahmood just before lunch as Tim Bresnan edged to Dane Vilas at first slip, leaving the score at 178 for five in the 56th over of the innings.
In fact, all 10 wickets in the Yorkshire innings fell to catches behind square on either side of the wicket, including eight to either keeper, the slips or gully.
Wicketkeeper Alex Davies also took a one-handed catch diving to his right to help Clark get rid of Ben Coad late in the innings.
It actually came two balls after Lyth was caught behind chasing a wide one from Clark in the 77th over - the next ball he faced after reaching 100 - as Yorkshire slipped to 249 for nine.
Despite their improved fortunes today, Lancashire’s first-innings 123 on day one meant they were always fighting to limit the damage.
And they have a mountain to climb having lost Davies, England Test opener Haseeb Hameed, Luke Procter and captain Steven Croft in their second innings.
Davies was first to go in an elongated evening session when he was trapped lbw by Jack Brooks, who had earlier added a useful 18 with the bat to help the hosts claim a second batting point.
That left the Red Rose at 23 for one in the tenth.
Hameed was next to go, also trapped lbw for 10, when Coad struck in the 15th - 33 for two.
Procter then edged Brooks to first slip in the 28th as the visitors slipped to 61 for three.
And it was 81 for four in the 33rd when a Croft edge against Ryan Sidebottom found Lyth at second slip.
Shiv Chanderpaul and Vilas then shared an unbroken 60 to ensure there was no further alarm for Lancashire.
They were faced with the first over of spin in the match when Azeem Rafiq bowled the penultimate over of the day and will begin day three on 43 and 22 not out respectively.