Forty of the top 50 players on the Official World Golf Ranking are scheduled to compete. World No. 4 Vijay Singh is among the absentees. He withdrew for the second-straight week due to a pulled rib muscle.
Included in the field is Southern California native Tiger Woods.
Woods, who played in his first PGA Tour event as a 16-year-old amateur in 1992, has never won the Nissan Open. Hes played five times as a professional, and finished runner-up twice. His best chance for victory came in 1998, when he lost to Billy Mayfair in a playoff.
Tiger, who won in his season debut in last week's Buick Invitational, withdrew from last years Nissan, citing fatigue. He had been sick the weeks prior and wanted to go home and rest before competing in the World Golf Championships-Accenture Match Play Championship, where he lost in the first round to Peter OMalley.
The international contingency includes Darren Clarke, Niclas Fasth, Sergio Garcia, Bernhard Langer, British Open runner-up Thomas Levet, Colin Montgomerie, Nick Price and Bob Hope winner Mike Weir.
Mattiace's victory a year ago was his first career tour title in his 220th start. He then won the FedEx St. Jude Classic four months later en route to finishing 18th on the money list.
Thus far this season, he has missed two cuts in four starts and has yet to break into the top 20.
'In the last month, (my game) hasn't been that good. And I struggled a little bit,' Mattiace said Tuesday. 'But I see things coming around. And I actually like the way I am swinging at the ball right now.'
Five players have successfully defended their title. Corey Pavin was the last to win back-to-back, in 1994 and 95.
This is the 77th playing of the event, and the 41st time that it will be contested at Riviera. Eleven different courses have been used over the years.