The blackout inside Qualcomm Stadium during an Aztecs game against Stanford was due to the lights being left on auto mode, the city confirmed.
San Diego State University beat the Cardinal 20-17 in Saturday night's game. But at one point in the game, the lights went out, leaving the players and the fans in complete darkness.
NBC 7 spoke to San Diego Gas & Electric previously and was told the problem was an independent issue was with the stadium lighting system, not something on the main grid.
Monday night, a City of San Diego spokesperson said the blackout was due to the lights being switched into auto mode, instead of manual.
On Saturday morning, stadium staff had been testing the electronics and put the lights into auto mode, which has a nine-hour cycle. After nine hours, the lights automatically turned off.
According to the city, the bulbs need at least 20 minutes to cool down before the lights can be turned back on.
"Unfortunately, it was during the SDSU-Stanford game," the city said in a statement.
The backup generators did kick in, keeping the scoreboard and several lights on the main concourse where fans sit lit up.
But there was a 22-minute delay in the game.