Glen Chapple finished with figures of 6-34 from 17 overs
Lancashire skipper Glen Chapple helped his team shade a busy wicket-taking day against Worcestershire at New Road.
Chapple took 6-34, backed by new ball partner Sajid Mahmood's 4-65, as the home side were shot out for 167.
The visitors then found themselves in a spot of bother at 73-4 in reply, thanks to three wickets from Liverpool-born Chris Whelan against his native county.
But Mark Chilton (51 not out), backed by Steven Croft's 43, helped Lancs to a slender lead by the close on 172-5.
Injury-hit Worcestershire, already without pacemen Simon Jones (knee) and Kabir Ali (hamstring), were further hampered when Ashley Noffke pulled out having aggravated the hip he had surgery on in the winter.
To add insult to injury, Chapple then took no time tearing out Stephen Moore, Daryl Mitchell and Ben Smith for a personal cost of just three runs.
Skipper Vikram Solanki, who walked to the wicket boasting 426 runs from six first-class innings, could add only another 22 before offering Mahmood his first wicket, a leg-side catch to wicketkeeper Luke Sutton.
At that stage, in their delayed first home Championship match of the season, Worcester were sinking fast on 36-4.
But Moeen Ali, dropped on 17 in the gully by Ashwell Prince off former Worcester loan signing Kyle Hogg, and Steven Davies added 88 in 17 overs - that one stand worth more than half the team's score.
Davies was trapped lbw for 48 by Chapple, who made it six scalps by quickly adding Gareth Batty and Moeen for 35.
Chapple's career-best 7-53, against Durham at Blackpool two years ago, looked under threat. But Mahmood stepped in to claim 9, 10 and jack.
Lancashire made an uncertain start in reply when Whelan removed Paul Horton lbw before also earning decisions against Prince and Tom Smith. And the visitors' discomfort continued just after tea with the loss of Francois du Plessis.
But Croft and Chilton helped the visitors earn a lead. And, despite Croft being removed by Matt Mason, Chilton and Sutton are still there overnight, intent on developing that small lead.
Worcestershire pace bowler Matt Mason told BBC Hereford and Worcester:
"I thought we started not as well as we could have done as there were a few too many four-balls.
"If we had kept enough balls in the right areas then we would have got a little bit more out of the pitch ourselves so there is a little bit there.
"When there are 15 wickets everyone assumes the pitch is unplayable but I think it was a combination of a little bit of poor batting and the wicket to a degree."
Visiting captain Glen Chapple told BBC Radio Lancashire:
"I thought we bowled really well after lunch, so I was pleased with that.
"We would have batted first because the pitch looks like it will deteriorate.
"It's nice to get a five-for early in the season. Everyone needs confidence, and I'm no different."
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