Manchester City 2 Manchester United 1
The night belonged to the Argentinian, who scored twice as City established a slender advantage in an exciting first leg encounter.
Tevez, who quit Old Trafford in the summer, made it nine goals in his last six City starts and 17 for the season as he provided the cutting edge which United have lacked since his departure and also the sale of Cristiano Ronaldo.
After their FA Cup exit at the hands of League One side Leeds, Sir Alex Ferguson was determined there would be no further slip as he fielded his strongest line-up against United's arch-rivals.
City's only surprise selection was 19-year-old central defender Dedryck Boyata, who was making only his third first-team appearance.
The City fans were silenced in the 17th minute as United broke the deadlock to seize the initiative as Ryan Giggs found the net with his first goal in the Manchester derby since 1996.
The veteran Welshman had a simple tap in from two yards after the ball rebounded into his path off keeper Shay Given, who had blocked Wayne Rooney's flicked shot.
City were handed an unexpected route back into the match five minutes before half-time when United conceded a penalty after Rafael Da Silva pulled back Craig Bellamy as he burst into the box .
Tevez stepped forward to smash home his 16th goal of the season from the spot.
Giggs would have regained the lead for United just short of the hour had Given not scrambled his close-range header to safety.
City went ahead for the first time midway through the second half when United failed to clear a Bellamy corner and Vincent Kompany hooked the ball back into the box for Tevez to head home from inside the six-yard box.
But in the latter stages, City had to desperately defend as United hunted an equaliser and Rooney was denied three times by excellent saves from Given.
Substitute Michael Owen had an effort cleared off the line by Nedum Onuoha as City somehow managed to hold onto their precarious lead.