Following a goalless draw in Milan, Portuguese midfielder Pele put Roberto Mancini's side ahead in the 52nd minute at the Stadio Olimpico before Julio Cruz capitalised on a goalkeeping error with seven minutes left to play.

Two minutes earlier, Nerazzurro defender Marco Materazzi had been sent off for a harsh foul on Goran Pandev.

Inter will face the winner of Thursday's tie between Roma and Catania. Roma lead 1-0 from the first leg.

With the Nerazzurri focused on clinching the Scudetto this weekend, Mancini rested several of his top players in view of Sunday's league encounter against Siena.

Inter struggled against a dominant Lazio, who had clear chances to score but were unlucky on the night.

Christian Ledesma struck the post early on before Tommaso Rocchi fired just wide of the far post midway through the first half.

Luis Jimenez should have put Inter in front before the break but he fired wide from close range.

Shortly after the restart, goalkeeper Francesco Toldo was forced to make a one-handed save from Rocchi's powerful header.

Just when Lazio looked more deadly, Inter broke the deadlock.

Pele fired past goalkeeper Marco Ballotta from David Suazo's low cross.

Shortly after the hour mark, coach Mancini was handed his marching orders for dissent following his sarcastic applauding of the referee.

Ledesma almost equalised on the hour mark but Toldo did well to fully stretch to clear the midfielder's left-footed strike.

Materazzi's sending off did not hinder Inter as soon after Cruz tapped in from Ballotta's poor clearance.

Inter captain Javier Zanetti could not hide his delight after the game.

"We really wanted this final and we are happy to have made it," he said. "I think we played well and now we must recover our energies in view of Sunday's game."

As for Lazio, coach Delio Rossi believes his team leave the competition with their heads held high.

"It's painful not to have progressed considering what we have done tonight," said Lazio coach Delio Rossi. "I think we deserved better, my players showed a lot of determination but it wasn't enough."