He struggled with his swing path through the strike zone, causing him to sometimes pop balls up when attempting to go to the opposite field.
His fly-ball, ground-ball and line-drive rates through the first month of play were similar to those in 2011, a season that saw him post career-worst marks with a .251 batting average and a .291 on-base percentage.
But May has been a much different story.
According to FanGraphs.com, Johnson's line-drive rate of 28.2 percent and ground-ball rate of 49.3 percent are the highest they have been during May. Also, Johnson's fly-ball rate of 22.5 percent is the lowest it has ever been at this time of year.
His numbers on batted balls this month are also in line with his rates last season: 27 percent line drives, 45.5 percent ground balls and 28.3 percent fly balls.
As a result, Johnson's BABIP (batting average on balls in play) this month is .386, slightly lower than his .394 BABIP in 2013.
"When I'm hitting fly balls, it's just not good for me," Johnson said. "I feel like there's a lot of hits with line drives and hard ground balls. I think things start to fall through and go through holes.
"When you hit the ball in the air in the big leagues, most of the time it gets run down and caught. I'm not a huge power guy, so my balls aren't going to fly out of the stadium. I like to stay on the ground hard and line drives and get my hits that way."
Although Johnson has enjoyed a successful month, he has walked only twice and struck out 20 times in May. His .309 OBP is only .016 points higher than his batting average in 94 plate appearances.
He has swung at 48.6 percent of pitches outside the strike zone in May, much higher than his 39.6 percent rate in April and his 40.7 percent rate last season. He believes that may have contributed to a 1-for-21 skid from May 17-21.
"When I'm swinging at balls out of the zone, I'm struggling," Johnson said. "If I can get balls in the zone and put good swings on them, usually good things happen when that happens, so that's what I've got to focus on."