Middlesex 176 for 3 (Robson 93, Malan 51*) v Derbyshire
Robson batted fluently for his knock of 93 from 163 balls, sharing a 90-run third-wicket partnership with Malan, who remained undefeated on 51 when bad weather brought proceedings to a premature close.
The Middlesex captain, who has been named in England's T20 squad for their tour of New Zealand, still requires another 16 to pass the landmark of 1,000 County Championship runs for the season.
Derbyshire exercised their right to bowl first and gained an initial success in the fifth over when Nick Gubbins pushed forward to Luis Reece and was caught behind without scoring.
Reece and Fynn Hudson-Prentice bowled tightly to squeeze Middlesex's scoring rate to around two an over, but Robson and Max Holden dug in as they gradually put together a partnership of 52.
However, Derbyshire struck again shortly before lunch when the pacy Sam Conners - making his first appearance at Lord's - unleashed a rising delivery that Holden could only deflect into the hands of Wayne Madsen at first slip.
Robson, who looked comfortable on both sides of the wicket, nudged a two to third man to pass 50 for the sixth time this season in the second over of the afternoon session.
Meanwhile, Malan - who hit a career-best 199 when the sides met at Derby earlier in the season - settled quickly at the crease, clipping Reece for a boundary through midwicket as the Middlesex total progressed into three figures.
The skipper survived an lbw appeal from Anuj Dal, who looked the pick of the Derbyshire bowlers, regularly getting the ball to fizz past the bat without any tangible success.
There was another close call for Malan on 34 when he edged medium-pacer Alex Hughes to slip, but this time Madsen - who is only five catches short of the Derbyshire record for an outfield player - spilled the chance.
Yet it was Hughes who made the breakthrough in his next over as Robson attempted to cut him and Harvey Hosein, standing up to the stumps, snapped up the edge.
Bad light prompted the umpires to call for an early tea soon afterwards but, when play resumed, Malan swiftly advanced to reach his half-century from 94 deliveries.
He and Martin Andersson moved their side's score along to 176-3 before a further deterioration in the light, coupled with the arrival of rain, halted play for the day.