Defending champion Levi Leipheimer maintained his lead Thursday in the Tour of California, while Canada's Dominique Rollin won the nearly 7-hour fourth stage from Seaside in rainy conditions. Rollin, the 2006 Canadian road-race champion, emerged from a lead group of seven riders with about 12 1/2 miles left and finished the 135-mile road race in 6 hours, 56 minutes, 8 seconds. Leipheimer, who assumed a 13-second race lead Wednesday, finished 16th in the main field, 2:28 behind the winner. He maintained the same margin over Fabian Cancellara (CSC) of Switzerland, the prologue winner and first of three race leaders.