Professional runners and jovial amateurs alike started out on the 7.46-mile course from the Embarcadero to Ocean Beach just before 7 a.m.
Teams of contestants in gold disco shorts, bumble bee outfits, tutus and more revealing costumes made their way west past Alamo Square and through the Panhandle.
Sunnyvale lawyer Aysha Pamucku, 26, dressed as the planet Saturn, took a break from walking the race near Alamo Square to take it all in.
"It moves in layers," Pamucku said. "Runners, then walkers, and then everyone else."
Despite a ban on drinking that went into effect at last year's Bay to Breakers, alcohol appeared to be openly and widely consumed along the race route today.
As of 11 a.m., police had arrested one contestant for public intoxication and resisting arrest, according to the San Francisco Police Department.
Officers had also given out eight citations for carrying open containers and possession of marijuana, police said.
The elite runners who were among the first to start the race had finished the competition by 8 a.m.
According to preliminary results, an Ethiopian woman was the first runner to cross the finish line
Manitu Daska, 28, -- last year's second fastest woman -- was the first to finish the course with a time of 39 minutes and three seconds, race spokeswoman Stephanie Reichin said.
Daska will take home a $37,000 cash prize for first place, Reichin said.
The second runner to cross the finish line was Sammy Kitwara, 25, of Kenya.
Kitwara's course time was 34 minutes and 41 seconds, but a time "equalizer" that allows the women's field to start the race about 4 minutes and 30 seconds before the men put him across the finish line just seconds behind Daska, Reichin said.
The equalizer is the difference between the course record for the best men's time and the record for the best women's time, Reichin said.
The second fastest runner in the men's field was Allan Kiprono, 22, of Kenya, who finished the race in 34 minutes and 49 seconds.
The second fastest woman was Diane Nukuri Johnson, 27, of Brundi, who finished with a time of 40 minutes and two seconds.