Yorkshire, replying to Somerset’s 399, have reached lunch on day two at Emerald Headingley on 56-2.
The White Rose wrapped up Somerset’s first innings inside eight overs of play starting as they advanced from 374-8.
Jack Brooks had Jamie Overton caught at third slip with the fifth ball of the day, finishing with figures of 5-116.
David Willey then had Jack Leach brilliantly caught one-handed at the second attempt by Lyth running back from second slip after a gloved short ball looped over his head.
Yorkshire lost Harry Brook 13 balls into their reply, bowled off his pad by Lewis Gregory as the score slipped to 5-1.
Lyth and Kane Williamson then shared 47 before the latter looped a catch to gully off a Craig Overton delivery which seemed to bounce a touch more than expected as the score fell to 52-2 in the 18th over.
Lyth will begin the afternoon on 20, with Gary Ballance for company on four.
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