Chelsea's midfielder Frank Lampard celebrates scoring against Blackburn Rovers during their FA Cup semi-final football match at Old Trafford in Manchester. Chelsea won the match 2-1. [AFP/Andrew Yates]

Chelsea beat Blackburn 2-1 with an extra-time winner from Michael Ballack in the FA Cup semifinal on Sunday to book a Wembley showdown with Manchester United.

Frank Lampard raced on to a Ballack pass and angled in a shot after just 16 minutes of a first half.

Jason Roberts leveled after break only to succumb to Ballack's goal on 109 minutes.

And the victory allowed Chelsea manager Mourinho head to the rebuilt Wembley aiming for his first FA Cup.

"It's a big, big final, between first and second in Premier League, between two semi-finalists in the Champions League," the Portuguese told Sky Sports.

There was a greater sense of urgency from both teams at the start of the second half and Chelsea should have put the game to bed within two minutes of the restart.

Ballack's incisive pass exposed the Blackburn offside trap, Drogba unselfishly squared the ball for Shevchenko, but the misfiring Ukrainian struck his shot against his standing leg and the chance was gone.

Rovers' equalizer came in the 64th minute when Roberts got the drop on Terry and dangled out a foot to divert Pedersen's free-kick past Petr Cech.

Blackburn were looking the more likely to settle the tie in normal time and only a magnificent save from Cech prevented Terry from heading Pedersen's long throw into his own net with only one minute to go.

The decisive goal came four minutes into the second period of extra time. Salomon Kalou's shot was blocked but the rebound fell to Ballack who drilled past an unsighted Friedel.

The blues, with the Carling Cup already in hand, kept alive their quadruple challenge as they are still in the hunt for the FA Cup, Premiership and Champions League.