Shrewsbury held off a second-half Derby fightback to cause a major Carling Cup upset in a gripping first-round tie at Pride Park.
Marvin Morgan struck twice in the first half, with strike partner James Collins on target in between, as the League Two side took a 3-0 lead into half time.
Chris Maguire gave hope to Derby when he headed in to reduce the arrears.
Tomasz Cywka set up Theo Robinson to cut the deficit to a single goal but the Shrews held on for victory.
Derby had enjoyed the majority of the possession in the early stages, but lacked any real punch up front.
In contrast, Shrewsbury were ruthless with every attack during the opening 45 minutes.
Against the run of play Morgan rose highest to power home Lionel Ainsworth's corner to give the visitors the lead, which Collins doubled when he scrambled home another Ainsworth cross.
Former County winger Ainsworth made it a hat-trick of assists three minutes later, crossing for Morgan to add his second and the team's third.
However, straight from the restart after half-time, Maguire headed in Ben Davies' left-wing cross to give County a foothold in the game.
Robinson's 78th-minute strike set up a tense finish but County were unable to force an equaliser as Shrewsbury bravely defended their lead.
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Derby County manager Nigel Clough told BBC Radio Derby:
"We know that we're at the stage where we can put out a team on the Saturday to compete, but if we lose a few players, then we're not as competitive.
"It was a great opportunity to get a couple of wins under our belts early in the season, two home wins, and it sets us up from there.
"Despite spending two days telling the players 'Shrewsbury will come here, they'll enjoy it, they'll revel in it, they'll run their socks off', maybe one or two of them thought, 'we don't have to put the effort in'."
Shrewsbury boss Graham Turner told BBC Radio Shropshire:
"It's been a terrific performance, although we made it nervy for ourselves after totally dominating the first half.
"At 3-0 up, we could and should have killed them off, but overall I've got to be pleased with the way we passed the ball about brilliantly and played well against quality Championship players.
"We were a real handful for them and deserved to go through."