Police say Denver, 24, was with his father, older brother and two other people a few blocks from the Giants' stadium after leaving the ballpark in the eighth inning of the Giants 6-4 victory when their group exchanged words with some Giants fans. The Giants fans didn't attend the game and had left a nightclub.
San Francisco police said Michael Montgomery, 21, of Lodi, was arrested on suspicion of homicide. Suhr said Montgomery made some "incriminating statements" while in custody that led to his arrest.
Another person, whose name was not released, was also taken into custody. Police said they were still looking for two more suspects.
But Montgomery's father said late Thursday that his son was jumped during the fight, and he stabbed Denver in self-defense.
Marty Montgomery told the Lodi News-Sentinel that his son said by phone that Denver, who was wearing Dodgers apparel, yelled, "Giants suck," at Montgomery's friend, who was wearing a Giants hat, when Denver and others hit his son and their friends without warning.
Marty Montgomery said that during the fight, Denver hit his son over the head with a chair, and in self-defense, his son, Michael, stabbed Denver.
"It was a self-defense deal," Marty Montgomery said. "(Michael) got jumped. (Denver and friends) started swinging chairs and he stabbed (Denver). (Denver) mouthed off about the San Francisco hat. It wasn't even (Michael's) hat."
The father said he had been trying to reach his son on Thursday when his son called him and told him about the fight.
"He's freaking out," Marty Montgomery said. "He's like, 'I saw him die in his dad's arms.'"
Denver was born in Los Angeles County but was living in Fort Bragg, about 170 miles north of San Francisco, his friend Matt Gomes said late Thursday. "He was an amazing guy who made everybody happy and made them laugh. He was there for everybody," Gomes said.
Denver apparently was trying to help a buddy who was getting beat up during the fight, Gomes said. "He was defending his friend," Gomes said. "And then he got stabbed and died."
Gomes said he doesn't believe Denver, his family and friends started the fight.
Janet Alvarado, Denver's aunt, told KNBC-TV in Los Angeles that Jonathan Denver was a "gentle, sweet boy." Speaking from her home in Covina, she called his death senseless and said she had no idea how it happened.
"I wish I could tell you how this happened, why this happened. I have no clue why anyone would do this to any family," she said.
Wednesday's fatal stabbing was the second violent confrontation between Dodgers and Giants fans in the past several years to end in death or serious injury. Bryan Stow, a Northern California paramedic and Giants fan, suffered a traumatic brain injury after two men dressed in Dodgers gear attacked him following the teams' March 31, 2011, game in Los Angeles. They are awaiting trial on charges in the beating, which sparked outrage and brought stadium security changes around the state and country.