Lees was 20 years and 95 days when he made 275 not out against Derbyshire – the joint 11th-highest innings in Yorkshire’s history, and the second-highest since the war.
Lees beat the record of Richard Blakey, who was 20 years and 225 days when he struck 204 not out against Gloucestershire at Headingley in 1987.
The tall left-hander batted for nine hours and 15 minutes, faced 436 balls and struck 38 fours and a six in a chanceless display.
Lees’s innings underpinned a total of 617-5 declared, the third-highest ever made at Chesterfield behind Yorkshire’s own 662 in 1898 and Durham’s 625-6 declared in 1994.
It was also the third-highest individual score at the venue behind Percy Perrin’s unbeaten 343 for Essex in 1904 and Jack Brown’s 300 for Yorkshire in 1898.
Having hit 677-7 declared against Derbyshire at Headingley earlier this summer, Yorkshire have racked up 1,294 runs in two innings against them at an average of 107.83 runs per wicket.
They went on to win the game at Headingley by an innings and 39 runs; they are well on course to win this one too, having reduced Derbyshire to 94-5 at the end of a second day Lees will never forget.
“I was really pleased with my performance,” said Lees, whose innings beat by one run the career-best of Yorkshire’s director of cricket Martyn Moxon, who scored 274 not out against Worcestershire at New Road in 1994.
“I just pipped Martyn as well, so to take him down was particularly pleasing.
“Andrew Gale almost did it earlier in the season when he got 272 against Notts at Scarborough.
“‘Galey’ didn’t know what ‘Frog’s’ highest score was, but, of course, ‘Frog’ told everyone when he just failed to beat it, which is why I knew I’d gone past it here.”
Lees resumed on 171 out of 367-2 on another glorious day in deepest Derbyshire.
There were a few more wispy white clouds than there were on day one, but the sky for the most part was brilliant blue.
No less glorious was the Yorkshire batting, Gale setting the tone with six boundaries in the first four overs.
Perhaps the pick was a cover-drive off Tim Groenewald which made a beeline for the sponsor’s marquee as surely as a thirsty corporate guest.
Gale, nine overnight, progressed to a fine half-century from 73 balls with nine fours.
The captain was within range of a fourth hundred in as many Championship games when he became off-spinner Peter Burgoyne’s maiden Championship victim, bowled for 74 attempting to sweep.
Gale’s dismissal after a stand of 138 with Lees in 30 overs was Derbyshire’s solitary success in an opening session in which Yorkshire scored 142 runs in 42 overs, Lees making 50 of them after reaching his double century from 321 balls with 30 fours.
With quick runs the name of the game in the afternoon, Gary Ballance injected impetus with four sixes during a sprightly 66 from 98 deliveries.
Ballance added 109 with Lees in 30 overs before being stumped giving Wes Durston the charge, Lees progressing to his 250 from 415 balls with 36 fours and then striking his solitary six when he lofted Groenewald over long-on.
But with Gale wanting to have a crack at the Derbyshire batsmen before tea, the captain pulled the plug when Adil Rashid was caught behind chasing a wide one from Mark Footitt.
Needing 468 just to avoid the follow-on, Derbyshire made a dismal start.
Chesney Hughes, who scored 270 when the sides met at Headingley, and whose team could have done with him repeating the performance, was lbw to Ryan Sidebottom in the seventh over.
Ben Slater and Wayne Madsen lifted the total to 52 before Steve Patterson claimed two wickets in three balls.
Madsen walked after being caught down the leg-side despite being given not out by umpire Jeff Evans, an act of sportsmanship for which he received a great hand from the 1,500 crowd, and which contrasted with the disgraceful antics of a certain England player in last week’s Trent Bridge Test.
Wes Durston was Patterson’s second victim, pinned lbw, before Jack Brooks turned the screw in the lead up to stumps with the wickets of Dan Redfern and Ben Slater, who were caught behind in successive overs.
White Rose top run-scorers
Highest individual scores in Yorkshire’s history:
341: George Hirst v Leics, Aylestone Road 1905
339: Darren Lehmann v Durham, Headingley 2006
315*: Percy Holmes v Middlesex, Lord’s 1925
313: Herbert Sutcliffe v Essex, Leyton 1932
311: Jack Brown v Sussex, Sheffield 1897
302*: Percy Holmes v Hampshire, Southampton 1920
300: Jack Brown v Derbyshire, Chesterfield 1898
285: Percy Holmes v Notts, Trent Bridge 1929
280*: Len Hutton v Hampshire, Sheffield 1939
277*: Percy Holmes v Northants, Harrogate 1921
275*: Alex Lees v Derbyshire, Chesterfield 2013
275: Percy Holmes v Warwicks, Bradford 1928