Marcus Harris entered the Leicestershire record books with a double-century as his side took complete control of their Vitality County Championship match against Derbyshire at the County Ground.
The opener struck 214 from 303 balls, the highest score by a Leicestershire player at Derby, as the visitors posted 574 for 7 on the second day of the Division Two match.
Harris shared a fourth-wicket stand of 153 with fellow Australian Peter Handscomb, who scored 68, before Ben Cox's 69 off 76 balls put the finishing touches to a tiring chase.
Needing 425 to avoid a follow-on, Derbyshire slumped to 12 for 3 and closed on a precarious 54 for 4.
Harris had been given two lives by Derbyshire on the first day and was given another early on the second morning.
Derbyshire had made the breakthrough they needed when Sam Conners found the right line to have skipper Lewis Hill caught at second slip, ending a stand of 90 off 135 balls for the third wicket. But the wicket they desperately wanted was Harris and they should have dismissed him on 88 when he edged Blair Tickner low to first slip where David Lloyd failed to hold on.
It proved another costly miss as Harris and Handscomb moved through the gears to exploit some inconsistent bowling.
Harris reached his century, Leicestershire's first of the season, from 189 balls, hitting Anuj Dal straight for his 13th four, and when Alex Thomson was finally brought into the attack in the 62nd over, he skipped down the pitch to drive it back over his head for another boundary.
The offspinner had taken 12 wickets in the previous match in Cardiff, but he could do nothing to stem the flow of runs as the Australian pair put on a 121-ball century stand.
Harris reached 150 off 235 balls before Handscomb cut Thomson for four to bring up his 50 before lunch and end a prosperous morning session for Leicestershire. They added 141 runs in 32 overs.
Derbyshire immediately took the new ball and, after Handscomb pulled Conners for six, he played around a full-length delivery from Tickner and was lbw.
Harris was out again on 167 in Tickner's next over when wicketkeeper Brooke Guest failed to take a low chance and he quickly moved to his double hundred, which came from 293 balls and included 26 fours.
He celebrated by hitting Thomson for a six and pulled Pat Brown for another maximum before playing over one from the fast bowler and losing his leg stump.
On his way out, Harris was congratulated by a number of Derbyshire fielders, although he might have been tempted to pass on his thanks given their generosity. And there was no respite for the home attack as Leicestershire secured the maximum with an over to spare and then opened up after tea.
Liam Trevaskis fell short of a half-century when he edged Luis Reece to deep midwicket. But Cox cleared the ropes twice as the lower order enjoyed themselves before the declaration.
That left Derbyshire with 18 overs to bat and, as often happens after a long spell in the field, they lost wickets. Harry Came was lbw to Tom Scriven off the third ball of the innings and Ben Mike struck twice in the space of two balls, having Reece caught at midwicket and then trapping Wayne Madsen with a leg-stump yorker.
An outstanding day for the visitors ended when Scott Currie broke Guest's defences to leave Derbyshire with a long way to go.