The Bruins, who had swept eight of their previous 10 conference matches and won the other two in four games, improved to 19-1 with their 17th consecutive victory and are 11-0 in the Pac-10. Arizona dropped to 12-7 and 6-5.
The Cats had three match points in the fourth game, but could not finish out the contest. It took UCLA until its fourth match point in game five to wrap up the victory.
Porter hit .409 with 19 digs. Sophomore outside hitter Ashley Bowles posted 19 kills, 19 digs and eight blocks.
Sophomore setter Dana Burkholder recorded her first career triple-double for the Cats. Her career-high 11 kills, 70 assists and 14 digs marked the 18th triple-double in Arizona history. Freshman outside hitter Lisa Rutledge matched her own team season-high in kills with 22, while junior middle blocker Marisa DaLee posted her career-best mark in kills with 21. Senior outside hitter Raelene Elam had 16 kills and 22 digs.
Arizona returns to action Tuesday when it plays host to No. 8 BYU at 7 p.m. in the McKale Center.