Ben Coad and George Hill claimed two early wickets but Worcestershire recovered strongly with the bat to move towards promotion on day one of the final LV=Insurance County Championship match of the summer at Headingley.
Worcestershire, having been inserted, fell to 22-2 and 67-4 amidst challenging conditions early on against the new ball.
When conditions eased in the sunshine later on, fifth-wicket pair Kashif Ali and captain Brett D’Oliveira shared 155 either side of tea as the visitors closed the day on 280-5 from 80 overs.
Kashif posted a confident career best 93 off 131 balls in only his fifth first-class appearance before offering a return catch to Dom Bess in the evening.
D’Oliveira went on to post 90 not out from 192 balls.
Yorkshire are aiming to secure a win which will give them a chance of avoiding finishing the season bottom of Division Two.
Worcestershire, meanwhile, started this fixture requiring just two points to secure promotion back to Division One, where they last were in 2018. That will be secured with them reaching 300 inside 110 overs.
Coad and returning Matt Milnes made an impressive start when play got going at 12.40pm following morning rain.
They caused Worcestershire’s top order problems under bright sunshine, with a host of plays and misses before Coad ousted Gareth Roderick and Azhar Ali courtesy of catches low down at third and second slip by Fin Bean and Adam Lyth.
That left the visitors at 22-2 in the ninth over.
Further success came quickly through Hill, who trapped opener Jake Libby lbw stuck on the crease for 32 and then had Jack Haynes caught by Bean going away to his right at third slip – 67 for four in the 20th.
Milnes deserved more reward for his endeavour, especially in his first six overs for 15, in only his second appearance for Yorkshire after a summer back stress fracture. He finished with figures of 0-46 from 14 overs.
The 29-year-old Nottingham-born bowling all-rounder has had the type of start to his Yorkshire career that you wouldn’t wish upon your worst enemy.
He signed from Kent at the back end of last August, only to suffer a stress fracture in his back in his final appearance for the Canterbury side.
Milnes worked hard through the winter with Yorkshire’s medical and fitness staff to regain full fitness, which he did in time to take four wickets and hit 75 in the season opener here against Leicestershire at the start of April.
Unfortunately, he was ruled out for five months with a relapse almost immediately after that fixture.
Milnes has played a trio of second-team fixtures over the last few weeks, with Ottis Gibson selecting him to appear here and give him and the county a late summer boost.
Worcestershire were on the ropes at four down early on today, but their cause was advanced in confident fashion by two similar innings from Kashif and D’Oliveira.
They both played some eye-catching strokes and were off-side dominant.
They recovered the score to 130-4 at tea and continued on after tea as Yorkshire found life difficult.
Kashif reached his second fifty of the Championship summer off 62 balls, while D’Oliveira – he is not quite recovered from a mid-August dislocated shoulder – followed him to his third fifty in as many matches off 78 balls inside the first half of the evening.
By that time, Worcestershire were 168-4 after 43 overs.
D’Oliveira went to 5,000 first-class career runs early in his innings. But Kashif missed out on a more significant career milestone – his maiden century.
He miscued a drive at Bess, who took a low catch going away to his left as the score fell to 222-5 in the 68th over.
D’Oliveira, dropped on 63 by Lyth at slip off Bess, and Ben Allison then batted through to close, sharing an unbroken 58. Allison is unbeaten on 31.
Their first port of call is 300 for promotion in the morning.