Middlesex 433 and 302 (Robson 67, Higgins 67, du Plooy 59, Thomson 4-115) lead Derbyshire 339 (Reece 125, Donald 54, Roland-Jones 5-81) by 396 runs
Middlesex captain Toby Roland-Jones tore through Derbyshire's tail with a five-wicket haul to put his side in control going into the final day of their Vitality County Championship clash with Derbyshire.
Seamer Roland-Jones finished with 5 for 81 - including four wickets in 19 deliveries - as the visitors, who began day three on 308 for 4, were hustled out inside the opening hour at Lord's for 339.
Having top-scored with 163 in Middlesex's first innings, Ryan Higgins played a supporting role with the ball, taking 3 for 60 before helping his side stretch their overall lead to 396 with a total of 302 second time around.
Higgins and Sam Robson both scored 67, with former Derbyshire skipper Leus du Plooy contributing 59 - his second half-century of the match - ensuring the visitors will need to break their record fourth-innings total to secure victory.
Trailing by just 125 with six wickets intact at the start of play, Derbyshire's prospects of a first-innings lead looked fair - but those swiftly evaporated as their batting was blown away by Roland-Jones and Higgins.
Luis Reece was first to depart for a season's best 125, caught behind prodding outside off stump at Higgins and, once the new ball had been taken soon afterwards, wickets began to tumble.
Aneurin Donald completed his second successive Championship half-century, advancing to 54 before Roland-Jones had him caught at short cover and the dismissal of Anuj Dal in the next over opened up the visitors' tail. Roland-Jones made short work of Derbyshire's last three, with Zak Chappell leg-before not playing a shot and Alex Thomson and Daryn Dupavillon both out to slip catches as the home side secured an advantage of 94.
Chappell immediately responded with the ball, slanting his opening delivery across Mark Stoneman to have the left-hander caught in the slips, but Robson put his first-innings duck firmly behind him with a series of confident strokes on both sides of the wicket.
The opener raced to his half-century before lunch, dominating a partnership of 85 with Max Holden, who was dropped on nought at second slip and took 25 minutes to get off the mark, but settled down to play a gritty knock.
However, Chappell struck again when Robson clipped him into the hands of midwicket and that, along with Thomson's consistent and prolonged spell of offspin from the Nursery End, helped Derbyshire to apply the brakes.
With Middlesex restricted to less than two-and-a-half an over during a lacklustre afternoon session, Reece's medium pace finally prised out Holden, who prodded to a close fielder five shy of his half-century. Reece also removed Nathan Fernandes, bowled having a swing soon after the tea interval and the home side seemed reluctant to commit to a change of gears as they trudged past 200.
Du Plooy's innings, which ended when he skied Thomson to deep midwicket, was watchful more than exuberant and, despite taking successive boundaries off the spinner, Higgins also looked unusually subdued.
Despite that, the allrounder brought up his half-century by hammering Thomson over mid-on for six, just after Dal's flying catch in the deep to remove Luke Hollman had provided him with a well-deserved second wicket. Thomson gained his third by having Roland-Jones caught at long-off, finishing the day with figures of 4 for 115 when Henry Brookes holed out in the final over.