The man, whose name was not released, collapsed during the third quarter. Stadium staff responded to a cardiac emergency and the man received CPR and was rushed to a hospital, where he was pronounced dead.
According to the AP, the man was sitting "in the sun-baked part of the stadium, near the top of the lower bowl behind the visitor's sideline, where temperatures reached 80 degrees and sent many fans to the shady concourses."
It was the third death at the stadium site, as two workers died during construction, reports the San Jose Mercury News.
"The 49ers organization is deeply saddened to hear of the passing of one of our fans earlier today," the team said in a statement. "We would like to extend our heartfelt condolences and prayers to his family and friends in this time of sadness."
- Molly Geary