Slow left armer Parkinson reached the milestone when he had Jack Haynes stumped shortly after tea to give him his third wicket of the innings.
The 24-year-old had limited opportunities previously in his career in red ball cricket and five campaigns had yielded only 54 wickets although he has been a key member of the Foxes T20 attack with a season’s best haul of 21 wickets in 2021.
But Parkinson has fully seized his opportunity this summer in the longer format although his side had to play second fiddle for long periods against Libby and Co as Worcestershire closed on 378-6 – a lead of 156.
He completed 1,000 runs for the summer on Tuesday evening and lifted his overall tally to 1,072, a figure only currently surpassed by Sussex’s Tom Haines.
Libby received excellent support from nightwatchman Charlie Morris, who scored his maiden Championship fifty, and there were useful contributions down the order.
Worcestershire resumed on 30-1 and Morris on nine was dropped at first slip off Chris Wright but it was one of few moments of alarm during the morning session for the second wicket pair.
Libby took advantage of some loose deliveries from Abidine Sakande to pick up three boundaries in one over.
Morris then repeated the same feat in an over from Wright before Libby reached a 72 ball half century with nine boundaries.
The century partnership came up in 30 overs and the last ball before lunch from George Rhodes enabled Morris to reach his fifty from 123 balls with his ninth boundary.
The morning session produced 108 runs from 30 overs but the picture changed after lunch.
Morris was beaten by a quicker delivery from Parkinson and bowled in the first over after the resumption without addition to his score.
The stand with Libby was worth 125 in 37 overs.
Wright bowled an impressive spell during the early part of the afternoon and was rewarded when Libby on 77 went back and looked to force the ball through the off side and nicked through to Louis Kimber at second slip.
Gareth Roderick had played two promising 40 plus knocks on a difficult pitch against Middlesex at Lord’s last week and he continued in the same manner as the first batting point was secured in the 65th over.
Roderick had moved onto 35 before he was dismissed in an unfortunate manner. He inside edged a delivery from Ed Barnes onto his boot and the ball ballooned up to Louis Kimber at second slip.
Parkinson struck in successive overs after tea as Brett D’Oliveira, 37, picked out short extra cover and Haynes on 44 was stumped after the ball bounced off keeper Sam Bates onto the wicket.
But Ed Barnard (44 not out) and Ben Cox (52 not out) overcame the second new ball – taken at 270-6 – and then pushed home Worcestershire’s advantage against a tiring attack during a century stand in 24 overs.
n Meanwhile, the Central Sparks came up short in their Rachael Heyhoe Flint Trophy semi-final eliminator against Northern Diamonds. Central Sparks captain Eve Jones said: “It’s disappointing to finish the way we have, but there has been lots of positives, finishing third and some excellent performances on the pitch.”