Reading came into 2005 boasting the only unbeaten statistic in the division but saw that run cruelly ended by a Derby side who specialise in wins on the road.
George Burley's Rams withstood an early battering by the home side and then pounced on the stroke of half-time with a poacher's strike from former Sunderland striker Smith.
Tom Huddlestone headed the ball down and Grzegorz Rasiak flicked it on into the path of Smith, who coolly rounded Reading keeper Marcus Hahnemann before slotting home.
It was a cruel end to the half for Reading, who had started so brightly as they looked to maintain their impressive home form.
Nicky Shorey's sweetly struck free-kick drew a fine save from Derby keeper Lee Camp, who also reacted smartly to take the ball off Nicky Forster's toes as the striker looked to take him on in front of goal.
Lloyd Owusu saw an early shot blocked and was denied the chance of a tap-in when James Harper overhit a seemingly simple cross and Reading were made to pay for the lack of a final ball.
Derby's win came on the back of two straight defeats and Burley's side have now won seven times on the road this season, having also put paid to Wigan's unbeaten home run.
Having withstood Reading's early pressure, Burley's midfield four began to take control and Smith served notice of their intent with a low drive that deflected onto a post.
Smith also teed up Rasiak, only for the Polish international to perform an embarrassing air shot with the goal at his mercy.
But it all came right for Derby's front two on the stroke of half-time and the visitors defended defiantly in the second half as Reading searched frantically for a way back.
Nicky Forster came within an inch of winning a penalty for Reading when Michael Johnson tripped him on the edge of the penalty area but the striker was also guilty of wasting a string of chances, including an overhead kick that flew over from close range.