Worcestershire 280 (Clarke 88, Patterson 3-34) and 221 for 6 (Whiteley 65*) lead Yorkshire 430 (Gale 164, Bairstow 139, Leach 4-139) by 71 runs
Yorkshire had just one run in reserve when they forced Worcestershire to follow-on at Scarborough yesterday and the visitors then showed great resolution in wiping out the 150 arrears to slow down the County Champions' bid to register a fifth consecutive victory.
The main thorn in their flesh was Sheffield-born left-hander, Ross Whiteley, who exactly a week earlier had thrashed an unbeaten 91 off 35 balls with 11 sixes and two fours in a T20 encounter at Headingley.
This time, in more orthodox fashion, he completed his first Championship half-century since September, 2013, and was still there at the close with 65 when Worcestershire were 221 for 6 and leading by 71. Yorkshire are still favourites to wrap up a win on the final day if the weather holds.
There were five overs to go before lunch when Worcestershire went out to bat for a second time and there was a quick success for Tim Bresnan when he pinned Richard Oliver lbw.
Bresnan would have struck again early in the afternoon if Alex Lees had not dropped Tom Fell at first slip before he had scored but he then resisted for a further hour with his captain, Daryl Mitchell.
As news filtered through of Jonny Bairstow's inclusion in the England side for the third Ashes Test, he positioned himself well under a top-edged hook by Fell off Jack Brooks' fourth delivery upon being called into the attack.
It was Brooks who also ended Mitchell's two-hour vigil when he edged him to Lees and Adil Rashid's leg-break bamboozled and bowled Joe Clarke to leave Worcestershire wobbling on 95 for 4.
But they were soon running smoothly again as Brett D'Oliveira and Whiteley combined in their side's highest stand of the match although it would have been terminated by Sidebottom if he had held on to Whiteley's drive to mid-on off Bresnan. Instead the batsmen were able to run two to level up the scores.
Whiteley's 50 came off 84 balls with eight fours before he drove Rashid wide of the pavilion for six but the delivery after the stand reached three figures D'Oliveira flicked Liam Plunkett to square leg and in the paceman's next over a rising ball to Ben Cox was fended to Jack Leaning at second slip.
Needing 281 for safety in the morning, a dashing last-gasp knock by Saeed Ajmal had rushed Worcestershire to 280 for 9 in their first innings when Bresnan replaced the expensive Plunkett and his third delivery thudded into Ajmal's stumps.
Ajmal, who had contributed 34 to a last wicket stand of 38 with Charlie Morris, blasted 37 from 30 deliveries with seven boundaries, five of which came in two expensive overs from Plunkett. They had resumed the third day on 195 for six with Clarke on 76 and Joe Leach 13. Clarke was soon boosting his score as he and Leach milked 24 runs off the first five overs from Plunkett and Brooks.
But a double bowling change quickly brought results and when Sidebottom replaced Plunkett he had Clarke caught at first slip by Lees for a career-best 88 from 125 deliveries with seven fours and a six.
Leach was lbw pushing half-forward to Adil Rashid who was driven for six into the pavilion enclosure by Jack Shantry but three balls later the left-hander was caught at silly mid-off by Lees.
In between being battered for five fours by Ajmal, Plunkett could only look on as Andrew Gale failed to hold on to a reflex catch at short leg that gave Morris a life at 269 for 9. It seemed as if the miss had saved Worcestershire until Bresnan intervened.
Yorkshire vs WORCS
LV= County Championship Division One
England Domestic Season