Ben Smith and Stephen Moore made Somerset pay for dropped catches on the second day of the Frizzell County Championship Division Two match at Bath.
Smith struck an unbeaten 107 -- his third ton in successive innings -- and Moore 86 as the County reached 328-4 in reply to Somerset's 408.
However, Ian Blackwell spilled both players at slip early in their innings, with Smith on 10 and Moore on 11. They proved costly errors as Graeme Hick's fluent 55 helped Worcestershire overcome the early loss of teenager Steven Davies.
Earlier, Somerset resumed on 359-8 and claimed maximum batting points courtesy of a ninth-wicket stand of 44 between Andy Caddick (19) and Matthew Wood, last man out for 127.
Seamer Matt Mason dismissed Wood to finish with 4-82, while Chaminda Vaas clean bowled Caddick to return with 3-88.
Worcestershire's reply began badly when 18-year-old Davies, on one, edged Caddick to Graeme Smith at first slip.
Hick looked in the mood for a big score though, taking four boundaries in an over off Simon Francis.
Hick and Moore took the score to 91-1 at lunch, with Hick reaching his half-century soon after the break, off 53 balls with nine fours and a six.
It was a major surprise when Caddick induced an edge with the total on 108 and Hick departed to Smith's second catch.
Moore's half-century occupied 66 balls and also featured nine fours, while Ben Smith reached the same landmark off 101 balls, with six boundaries.
Left-arm spinner Blackwell atoned for his earlier missed catches to dismiss Moore caught low down by Smith, leaving the visitors 220-3.
By then Worcestershire's Smith was well set and, after tea, he brought up his hundred, coming off 195 balls with 14 fours.
Zander de Bruyn contributed 30 before being pinned lbw by Richard Johnson. That brought in Gareth Batty, who ended unbeaten on 16 and was replaced by 12th man Daryl Mitchell today.
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