With new manager Nigel Clough watching on from the stands, the Rams, 18th in the second tier, produced a superb performance which earned them a slender but precious lead to take to Old Trafford for the second leg in a fortnight.

Scottish international Commons capped a man-of-the-match performance with a superb winner, smashing home a 25-yard rocket on the half-hour mark.

United however, abject though they were, will fancy their chances of turning around the deficit but Sir Alex Ferguson will know that a vastly-improved performance is needed if they are to reach Wembley.

The Rams made a bright start and went desperately close to grabbing the lead twice early on. Nemanja Vidic produced a superb clearance from off the line with Steve Davies waiting to pounce after Tomasz Kuszczak had blocked the winger's first effort in the eight minute, 120 seconds before Jonny Evans had to volley clear Mile Sterjovski's effort from underneath his own crossbar.

Paul Green made a good block from John O'Shea's shot as United finally found some attacking fluency in the 27th minute, but it was the Rams who grabbed a deserved lead soon after.

Sterjovski's pass from the right found Commons, and as the United defence backed off, the former Nottingham Forest midfielder unleashed a drive which flew past Tomas Kuszczak into the Polish keeper's bottom left corner.

Paul Scholes was off target twice in quick succession as United looked to strike back, but their flat and laboured attacking play failed to breach the Derby defence, with former Red Devils keeper Roy Carroll remaining largely untested.

Ferguson introduced Wayne Rooney and Cristiano Ronaldo on the hour mark in an effort to inject some life into his side and the Portuguese winger nearly dragged his side level twice within 60 seconds around the 75-minute mark.

First, the European Player of the Year drove a low effort from the edge of the box wide of Carroll's left-hand post, before lashing a free-kick from the edge of the box inches wide of the same upright soon after.

The Rams, understandably, dropped deeper and deeper but David Lowe's side could and should have extended their lead with 10 minutes remaining.

Commons turned Evans brilliantly before cutting in from the right and attempting to curl the ball around Kuszczak. The United keeper parried Commons' effort but only into the path of Rob Hulse, who blazed over the bar from eight yards with the goal at his mercy.

Green then fired narrowly over in the final minute of added time as the Rams comfortably held on for a superb victory.