Flowers missed last week's win over Seattle with a groin injury, while Allen was also dealing with a groin injury. Linebacker Jerry Attaochu (hamstring) and safety Jahleel Addae (hamstring) are also active.
Buffalo will again be without starting linebacker Keith Rivers, who suffered a groin injury in the opener in Chicago. The Bills will have wide receiver Robert Woods. And tight end Lee Smith makes his season debut after missing two games with a toe injury.
Running back Bryce Brown and tight end Chris Gragg are among Buffalo's inactives. Cornerback Ross Cockrell, linebacker Randell Johnson and offensive linemen Cyril Richardson and Cyrus Kouandjio also won't play.
On Saturday, the Chargers placed linebacker Melvin Ingram on the injured reserve, designated to return list.
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