David Villa, Santi Cazorla, Marcos Senna also scored for Spain, but Dani Guiza missed. Fabio Grosso, Mauro Camoranesi scored penalties for Italy.

Spain will face Russia in the semifinals on Thursday.

After a mostly dull 90 minutes at Ernst Happel Stadium, David Silva hit a shot just wide for Spain in extra time and Di Natale had a header tipped over the bar by Casillas.

Italy made its last substitution in the 108th, bringing on Alessandro Del Piero, but the team's continued caution suggested this was more for the shootout than for his ability to conjure a winning goal.

Spain created more openings in the first 90 minutes, but Italy went close in the 61st minute when Camoranesi had a goalbound shot blocked by the legs of Casillas.

With key midfielders Andrea Pirlo and Gennaro Gattuso suspended, the World Cup champions seemed mostly content to try and stifle a Spain team that had shown some of the best attacking football in the group stages.

Spain's best opportunity came in the 81st when goalkeeper Gianluigi Buffon spilled a fierce long-range shot by Senna. The ball squirmed out of his hands and rolled back to hit the post before landing softly back in his arms.

The first half had been so poor that both sets of fans jeered the teams off the field for the interval, with the most noise the heavily outnumbered Italians made coming when Antonio Cassano took a 40th-minute corner right in front of them.

Spain at least attempted some enterprising football and had 10 shots to Italy's two, but the Italians' defense was so secure that only a blocked effort by Silva came from inside the area.

The move that led to that chance was arguably the brightest spot in a stultifying first half. David Villa set up Silva with a back-heeled return pass so audacious that even retired France great Zinedine Zidane, who was watching from the stands, nodded in approval.

Spain tried to quicken things up, refusing to dither over goal kicks and throws, but the game continued to succumb to Italy's leaden pace.

Silva twice had 25-meter (yard) shots saved by Buffon low to his left and the Spanish, who had flourished in the first round with eight goals in three first-round matches, seemed to get frustrated.

Silva was lucky not to get a yellow card in the 42nd when he threw himself over the outstretched leg of Grosso on the edge of the area. Silva writhed about on the gra** until play was halted, at which point referee Herbert Fandel marched half the length of the field to order him to his feet.

The pace improved at the start of the second half even if the quality didn't.

Fernando Torres and Villa worked the ball to Andres Iniesta on the left of Italy's area only for the midfielder to mis-control and let it hit his hand.

And Silva got a chance in the 49th when a clearance under pressure by Christian Panucci hit De Rossi and rebounded to Silva in the area. Silva twisted to get his shot away, but Giorgio Chiellini blocked with a sliding challenge.

But at least there seemed to be more attacking intent from Italy, which almost took the lead in the 61st after Luca Toni hooked the ball away from Casillas just as he was about to grab it. Camoranesi, who been on the field just three minutes, shot from in front of goal only for the recovering Casillas to block with his legs.

Villa was unlucky to be booked when the referee misinterpreted his slip in the area as a dive, but the fortune went Spain's way later on when Grosso was preparing to meet a cross into the area with a shot on goal, only for Toni to redirect the flight of the ball away from him with an attempted overhead kick.

Chiellini, who has only been starting in Italy's defense because he injured captain Fabio Canavarro in training before the tournament, had a stellar match throughout and blocked an effort by Guiza at the start of extra time.

Silva put the rebound just wide before, at the other end, Di Natale went close with his fierce header from a right-wing cross. Buffon then blocked a low shot by Villa, the last meaningful effort of the match.

Lineups:

Italy: Gianluigi Buffon, Gianluca Zambrotta, Christian Panucci, Fabio Grosso, Giorgio Chiellini, Simone Perrotta (Mauro Camoranesi, 58), Daniele De Rossi, Alberto Aquilani, Massimo Ambrosini, Luca Toni, Antonio Cassano (Antonio Di Natale, 75).

Spain: Iker Casillas, Sergio Ramos, Carles Puyol, Carlos Marchena, Joan Capdevila, Xavi Hernandez (Cesc Fabregas, 60), David Silva, Marcos Senna, Andres Iniesta (Santi Cazorla, 59), David Villa, Fernando Torres (Daniel Guiza, 85).