Investigators say the driver was delivering at a convenience market in San Bernardino, when he caught the teens looking through his truck.
He confronted one of the teens who was in the driver's seat and was stabbed from behind by the other teen. The teen in the seat then stabbed him several times.
Customers at a nearby restaurant witnessed the attack and chased way the attackers and helped the driver until emergency crews arrived at the scene.
Based on witness descriptions, police arrested two suspects about a block from the store.
The teens could face attempted murder charges.