In 1979, his only full season as a starter in San Francisco, DeBerg led the NFL in completions (347) and pass attempts (578). He ranked fifth in the league in passing yards (3,652), throwing 17 touchdowns against 21 interceptions. DeBerg had his first 300-yard passing game in his sixth start against Seattle, completing a season-high 31 of 40 passes for 306 yards with one touchdown and one interception. Later that year, he posted his first 100.0 passer rating as a starter (one of two 49ers' wins all year) against the Tampa Bay Buccaneers. DeBerg finished the game with 22 completions in 30 pass attempts (a season-high 73.3-percent completion rate), with one touchdown and no interceptions.