Updated at the bottom: An arrest has been made. The Dodgers say the victim was the son of a team security guard. Plus, the mayor's office issues a statement. First posted at 2:05 p.m.

San Francisco police planned to beef up patrols in the city tonight in the wake of Wednesday's fatal stabbing death of a Dodgers fan, which happened not long after L.A.'s loss on the Giants' home turf. It's the Dodgers' last game against San Francisco in the Bay Area this season.

See our coverage of the 2011 near-fatal beating of Giants fan Bryan Stow in Los Angeles here.

S.F. undercover cops will be dressed up in Dodger blue not only in and around AT&T Park but in the South of Market nightlife zone where 24-year-old Jonathan Denver was fatally stabbed following a pair of confrontations in the street, San Francisco police Sgt. Daneille Newman told L.A. Weekly:

Denver was wearing unspecified Dodgers gear when he was attacked, she said, but it wasn't clear if the dispute was over team loyalty.

The crime was reported about 11:39 p.m. at Third and Harrison streets, Newman said. The victim had gone to the game with his brother, his father and the father's girlfriend, she said.

They left during the eighth inning and had been at a “venue” in the SoMa area before hitting the street about 90 minutes after they left AT&T Park, Newman said. That's when two groups clashed for reasons unknown, she said.

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The two groups initially walked away from it, the sergeant said, but then “one of the parties couldn't let it go and the physical altercation took place.”

Newman was taken to San Francisco General Hospital where he was pronounced dead, she said.

Police happened to be in the area on extra patrols as part of the department's protocol for rivalry sports matches, she said:

They were still out and about and that's probably why these suspects were taken into custody.

Two men, ages 21 and 18, were detained for questioning, Newman said. They had not been arrested or booked, and cops were still searching for two additional suspects as well as for the murder weapon, she said.

Detectives also were canvassing the area for security video of the confrontations. They want anyone who might have captured cellphone video of the scene or its aftermath to call investigators at 415-553-1146.

Newman said that, along with the department's normal “rivalry package” of beefed-up patrols, there would be even more police on the street for tonight's second game between San Francisco and Los Angeles.

We want to make sure these rivalries stay on the field. There's not a place for this kind of rivalry in the city.

[Update at 2:50 p.m.]: The victim was the son of a security guard who works at Dodger Stadium, the team's Jared Kaufer told the Weekly.

He said it wasn't clear to the team if Denver was with his dad last night, which would be the case if what San Francisco police told us is true.

The security guard does not work away games, Kaufer said. It would appear the victim and his family members were in San Francisco to enjoy the game.

[Added at 4:12 p.m.]: Yusef Robb, spokesman for L.A. Mayor Eric Garcetti, sent us this statement:

It's just not worth it. There's nothing wrong with rivalry, but we have to keep things in perspective and let the players be the ones who battle it out on the field.

[Update at 5:56 p.m.]: One of the two aforementioned suspects has been arrested and booked on suspicion of homicide, SFPD's Newman told us.

He's 21-year-old Michael Montgomery of Lodi.

It's not clear what will happen to the second suspect, she said.

The San Francisco chief, Greg Suhr, told reporters today that at least of the two incriminated himself during questioning.

At least one person who was part of the attack was reportedly wearing a Giants cap.

-With reporting from LA Weekly staff writer Gene Maddaus.

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