The Bruins carry a 5-1 Pac-12 record into a three-game road series against the Cougars.
Ty Moore launched the game-winning three-run home run, his second of the year, in the 13th inning.
The Bruins are undefeated (4-0) in midweek games this year and have topped SDSU four-straight times.
Ty Moore and Trent Chatterton each hit their first home run of the season in the victory.
Grant Watson, Tucker Forbes, Grant Dyer & David Berg combined to allow just three hits and no runs.
UCLA's 19 hits are the most in a single game for the Bruins since April 14, 2012 at Arizona.
Bruin baseball player hit .571 in four games, including the game-winning home run on Friday.
The Bruins (14-5, 2-1) continue Pac-12 play this weekend with a three-game series against the Utes.
Trent Chatterton delivered the 13th inning walk-off sac-fly to give UCLA the series clinching win.
Chris Keck & Kevin Kramer each had two hits and Griffin Canning struck out six in four innings.
Information about getting in to Jackie Robinson Stadium for Sunday's game versus Washington.
James Kaprielian allowed no runs and struck out a season-high ten batters in the victory.