(CNN) -- Manchester United shattered Derby's Wembley dream to make a League Cup final date against holders Tottenham or Burnley following a dramatic conclusion at Old Trafford.
Carlos Tevez celebrates scoring as Manchester United win through to the League Cup final at Wembley.
The world champions were on cruise control after scoring three times in the first half at Old Trafford to overturn a 1-0 first leg semifinal deficit against their Championship rivals.
But United had to step up a gear in the closing stages after Giles Barnes converted an 80th minute penalty -- and then added a second direct from a freekick in time added on.
Unfortunately for Derby, substitute Cristiano Ronaldo had converted his own spot kick reply for United after 88 minutes, United winning through 4-3 on aggregate.
World player of the year Ronaldo drilled his penalty low into the bottom left hand corner after goalkeeper Roy Carroll was adjudged to have upended Argentine star Carlos Tevez.
But Derby, looking for their first win under new manager Nigel Clough, battled to the end with Barnes dropping his set piece inside the left hand upright.
Derby had the first effort on goal in the seventh minute when Kris Commons, scorer of the only goal in the first leg at Pride Park, was only just wide of the mark from 30 yards.
Nani showed him the way after 16 minutes. The winger picked up the ball on the halfway line, cut in from the left and, with no challenge forthcoming, smashed a dipping shot beyond keeper Carroll.
Six minutes later United were ahead overall when left-back John O'Shea found himself with plenty of time to slot home following good work by Tevez and Danny Welbeck.
The third came in the 34th minute. Giggs played the ball short to Rafael whose teasing cross was just right for Tevez to head home.
Brazilian defender Rafael could have added a fourth before the break. He fired into the side netting after exchanging passes with Giggs and was replaced by Darren Fletcher shortly afterwards after picking up an injury.
United's defensive problems increased when Jonny Evans suffered a problem 18 minutes from time that left him limping badly.
There were more worries for United supremo Alex Ferguson -- through to his 14th domestic final as manager -- with knocks for Nani and Anderson who left on a stretcher after the final whistle.
Tottenham take a 4-1 lead to Burnley in the second semifinal on Wednesday hoping to clinch a Wembley return on 1 March.