Outstanding Ronaldinho's Hat-trick
Portuguese midfielder Deco scored the other goal with another beautiful free kick shoot. He was also on target for the Catalans who were pegged back when defender Felipe stabbed in at the far post midway through the first half.
Ronaldinho restored Barca's lead when he stroked the ball inside the far post after Samuel Eto'o had cut a pass back from the byline.
And midfielder Deco made it 3-1 with another superb curling free kick just before the break.
Udinese were reduced to 10 men at the start of the second half when midfielder Vidigal was sent off after picking up a second booking.
And Ronaldinho completed his hat-trick with a final minute penalty after he was brought down by bemused Felipe as slipped past him into the area.
The win left Frank Rijkaard's side top of Group C with a maximum six points from two games. Udinese are second on three points.
It was also a triumph for the Dutchman's policy of rotating his squad after he had rested Ronaldinho and Deco for the 4-1 victory over Real Betis at the weekend.
"The boss knows what he's doing," said Brazilian Ronaldinho. "We understand his policy and he has our full confidence.
"The team played very well and I was delighted to help out with three goals."