The visitors grabbed a first innings lead of 112 when Matthew Hoggard took the last Somerset wicket without addition to their overnight score of 326. The former England seamer finished with 5-82.

Somerset looked to be fighting back when first innings centurion Jacques Rudolph fell for a second ball duck and Anthony McGrath followed to make it 58-2.

But Sayers was dropped on 30 and went on to a hundred off 208 balls, with 15 fours.

Adam Lyth was also given a life on three and progressed to 71 before Yorkshire closed on 329-5, with a lead of 441.

Sayers was out to the last ball of the day for 152 and Jonathan Bairstow ended 54 not out.

The dropped catches cost Somerset dear as they could have had their opponents 62-4. First James Hildreth spilled a straightforward chance at gully off Andy Caddick to reprieve Sayers and then Justin Langer failed to grab an edge offered by Lyth to slip off Arul Suppiah.

McGrath had been spilled by Suppiah at point on 25, but failed to add to that tally before being bowled by Willoughby, who had also removed Rudolph through a catch at second slip.

Somerset's inept fielding allowed Yorkshire to lunch at 67-2 and the afternoon session belonged to Sayers and Lyth, who gave no more chances.

Sayers reached 50 off 142 balls, with eight fours and Lyth followed, his half-century coming off 84 balls, with a six and six fours.

The partnership of 122 in 37 overs was finally broken by David Stiff, who added to his four first innings victims by having Lyth caught behind off a thin edge as he attempted a pull shot.

Tea was taken at 189-3 as the first rain of the match fell. But it quickly cleared and Yorkshire progressed to 221 before Adam Gale was well caught low down by Marcus Trescothick at backward point off Alfonso Thomas for 16.

Yorkshire had progressed sedately, but Sayers and Bairstow increased the tempo in the closing overs to set up a declaration in the morning, the latter racing to 50 off 52 balls, with nine fours.

Sayers reached his 150 shortly before the close, having faced 272 balls and extended his boundary count to a six and 20 fours. It was not a spectacular innings, but a vital one for his side as they looked to end a run of 17 first class games without a victory.

He was bowled by Zander de Bruyn off the first ball of the final over of the day to end play.

Read Chris Waters' report from day two at Taunton >>

Keep checking the website for updates throughout the day.