Johnson played his rookie season with the Athletics in 2005, batting .275 with 15 home runs and 58 RBIs.
He struggled early in 2006, batting .237 before being demoted to the A's Triple-A Pacific Coast League affiliate, the Sacramento River Cats, in July.
He returned to the A's roster on August 31, and finished the season with a .234 batting average, 9 home runs, and 37 RBIs.
It was later discovered that he suffered from double vision due to getting suntan lotion in his eyes, and he was able to clear up the problem for the 2007 season.

Johnson was expected to be the A's starting first baseman in 2007, but suffered a torn labrum in his hip late in spring training and missed the first three weeks of the season.
He returned April 25 and proceeded to get a hit in 16 of his first 18 games.
He was named American League co-Player of the Week with teammate Jack Cust for the week of May 7–13.
After the hot start, Johnson fell into a slump that lasted the rest of the season and plummeted his batting average to .236.
His worst month was July, in which he batted just .156 (10-for-64 in 19 games) with two home runs and eight runs batted in.
On April 9, 2008, Johnson was designated for assignment.
Johnson played his rookie season with the Athletics in 2005, batting .275 with 15 home runs and 58 RBIs. He struggled early in 2006, batting .237 before being demoted to the A's Triple-A Pacific Coast League affiliate, the Sacramento River Cats, in July. He returned to the A's roster on August 31, and finished the season with a .234 batting average, 9 home runs, and 37 RBIs. It was later discovered that he suffered from double vision due to getting suntan lotion in his eyes, and he was able to clear up the problem for the 2007 season.
Johnson was expected to be the A's starting first baseman in 2007, but suffered a torn labrum in his hip late in spring training and missed the first three weeks of the season. He returned April 25 and proceeded to get a hit in 16 of his first 18 games. He was named American League co-Player of the Week with teammate Jack Cust for the week of May 7–13. After the hot start, Johnson fell into a slump that lasted the rest of the season and plummeted his batting average to .236. His worst month was July, in which he batted just .156 (10-for-64 in 19 games) with two home runs and eight runs batted in. On April 9, 2008, Johnson was designated for assignment.
Dan Johnson (baseball)