AC Milan's Gianluca Zambrotta (R) lies on the ground with his feet in the air as Barcelona's Lionel Messi runs past with the ball during their Group H Champions League soccer match at the Nou Camp stadium in Barcelona, Sept 13, 2011. [Photo/Agencies]

Saviour Messi

Around 90,000 home fans packed into a sultry Nou Camp were stunned into near-silence seconds after the start when Brazil striker Pato left the home defence for dead and beat goalkeeper Victor Valdes with a low shot.

With captain Carles Puyol only declared fit this week after knee surgery and his partner in central defence Gerard Pique sidelined, Guardiola deployed midfielders Sergio Busquets and Javier Mascherano at the back.

The decision immediately appeared to have backfired when pacy Brazil striker Pato exposed their obvious lack of pace.

Straightaway Barca created a slew of chances for an equaliser before World Player of the Year Lionel Messi, after striking a curling freekick against the post, once again came to the rescue.

The Argentina forward, top scorer in the competition the past three seasons, danced through the Milan defence to the byline and squared for Pedro to rifle home with goalkeeper Christian Abbiati stranded.

Barcelona's David Villa celebrates scoring against AC Milan during their Group H Champions League soccer match at the Nou Camp stadium in Barcelona, Sept 13, 2011. [Photo/Agencies]

Barca had recovered their customary poise and a goal had long been coming when Villa stepped up to crack the ball into the top corner from 30 metres.

The home side were in total control without really threatening to score a third until fullback Eric Abidal conceded a stoppage-time corner, although the France international claimed he had been fouled.

Dutch midfielder Clarence Seedorf swung the ball over for Silva to claim an unlikely point.

"When they score an equaliser in the last minute you are left looking a bit stupid," Barca's Brazil fullback Daniel Alves told Spanish television. "We have to pick ourselves up and keep working."