Josh Allen underthrew Stefon Diggs with 12:18 remaining in the third quarter, and safety Alohi Gilman picked it. The Chargers used it go to 41 yards in eight plays for a field goal to pull them within 14-13.
Allen, though, answered.
He threw a 36-yard pass to Gabe Davis to set up 1-yard touchdown run three plays later.
The Bills now lead 21-13.
Allen had a 2-yard touchdown run in the first half and threw a 57-yard touchdown pass to Davis, who now has 130 yards on four catches.
Allen is 11-of-16 for 186 yards with a touchdown and an interception.
