Nick Gubbins, a 20-year-old left-hander from Richmond, made 54 on his LV= County Championship debut as Middlesex reached 280 for three on a weather-affected first day in their Division One match against Northamptonshire at Lord's.
Gubbins, given his chance because England's management have chosen to rest Sam Robson from this round of championship games along with most of the Test team beaten by Sri Lanka at Headingley, put on 128 with Chris Rogers for Middlesex's first wicket after Northants captain Stephen Peters had chosen to bowl first.
Australia opener Rogers made 86 to take his championship run-tally this season to 907 at an average of 69.76, and Dawid Malan also flourished later with 72 not out on an afternoon interrupted by four stoppages for rain.
Eoin Morgan, in need of runs to push his own England Test claims, survived a sketchy start to reach 27 but was then bowled by Andrew Hall soon after the fourth weather delay.
Northants, adrift at the bottom of the Division One table with seven defeats from eight matches, tried hard with the ball after seeing a green tinge in the pitch but they could not take a couple of early chances to split Rogers and Gubbins and paid the price on another sobering day for them in the championship top tier.
Radley School product Gubbins, calling for a sharp single into the off side to get off the mark, would have run out Rogers if a throw at the stumps had hit, and then on eight he was dropped by Matt Spriegel in the gully off Muhammad Azhar Ullah.
It was a let-off the youngster gratefully received, pulling Maurice Chambers for six - to the longest boundary on the Grandstand side of the ground - to go to 36 and past his previous best first-class score of 31 not out, which he made in one of eight innings for Leeds-Bradford MCCU.
At lunch he was on 43, with Rogers having already completed his half-century and Middlesex in control at 105 without loss.
Gubbins went to his own 105-ball fifty early in the afternoon session, driving with some power down the ground and through the covers, before attempting to pull Azhar from the last ball of the 38th over and skying to mid-on.
Malan was quickly into his stride and 40 runs had come in eight overs for Middlesex's second wicket, and with ominous ease for Northants' bowlers, when Rogers perhaps over-confidently aimed a drive at a full ball from Steven Crook, delivered from around the wicket, and was bowled after a 152-ball stay.
Crook deserved some reward for working up a decent pace and he was perhaps the pick of an ordinary-looking Northants attack, twice beating Morgan early on outside the left-hander's off stump.
Malan, on 32, was dropped at second slip off Hall, although Rob Keogh was almost at full stretch as he dived to his left to try to pull off the catch. Despite the loss of Morgan after a stand of 62 in 18 overs, Malan kept Middlesex moving forward with a purposeful innings featuring 12 fours from 112 balls.
By stumps Neil Dexter, with an unbeaten 19, had helped Malan to add a further 50 for the fourth wicket and ensure Middlesex took the opening day honours.
Gubbins said: "I am obviously absolutely delighted to get past 50 on my championship debut.
"When I woke up this morning I was pretty nervous, but this is what you work hard for when you are young and trying to develop your cricket."