Derbyshire 54 for 4 (Mike 2-14) trail Leicestershire 574 for 7 dec (Harris 214, Handscomb 68, Cox 69) by 520 runs
Marcus Harris entered the Leicestershire record books with a double-century that gave his team complete control of the Vitality County Championship match against Derbyshire at the County Ground.
The opener plundered 214 from 303 balls, the highest score by a Leicestershire player at Derby, as the visitors racked up 574 for 7 declared on the second day of the Division Two game.
Harris shared a fourth-wicket stand of 153 with fellow Australian Peter Handscomb who scored 68 before Ben Cox tucked into a tiring attack with 69 from 76 balls.
Needing 425 to avoid following-on, Derbyshire slumped to 12 for 3 and closed on a precarious 54 for 4.
Harris had already been given two lives by Derbyshire on the first day and he was handed another reprieve early on the second morning.
Derbyshire had got the breakthrough they needed with Sam Conners finding the right line to have skipper Lewis Hill caught at second slip which ended a stand of 90 from 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 cling on.
It proved another expensive miss as Harris and Handscomb moved through the gears to plunder some inconsistent bowling.
Harris reached his century, the first of the season for Leicestershire, from 189 balls by straight-driving Anuj Dal 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 him back over his head for another boundary.
The offspinner had taken 12 wickets in the previous match at Cardiff but he could do nothing to stem the flow of runs as the Australian pair cruised to a century stand off 121 balls.
Harris reached 150 from 235 balls before Handscomb cut Thomson for four to complete his 50 before lunch and end a prosperous morning session for Leicestershire who added 141 runs in 32 overs.
Derbyshire took the new ball immediately and after Handscomb pulled Conners for six, he played around a full length ball from Tickner and was lbw.
Harris was dropped 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 contained 26 fours.
He celebrated by driving Thomson for six and pulled Pat Brown for another maximum before he played across one from the fast bowler and lost his leg stump.
As he walked off, Harris was congratulated by a number of Derbyshire fielders although given their generosity, he may have been tempted to pass on his thanks. And there was no respite for the home attack as Leicestershire secured maximum batting points with an over to spare and then opened up after tea.
Liam Trevaskis missed out on a half-century when he pulled Luis Reece to deep midwicket but Cox cleared the ropes twice as the lower order enjoyed themselves before the declaration came.
It left Derbyshire with 18 overs to negotiate and, as so often happens after a long spell in the field, they lost wickets. Harry Came was lbw to the third ball of the innings from Tom Scriven and Ben Mike struck twice in two balls having Reece caught at midwicket and then trapping Wayne Madsen with a leg stump yorker.
An outstanding day for the visitors ended with Scott Currie defeating Guest's defensive push to leave Derbyshire with a long road ahead of them.
