League, an All-Star closer last year, allowed runners to score in four of his first seven Dodgers appearances. He gave up nine hits in five innings with five strikeouts and three walks.
But with the counsel of pitching coach Rick Honeycutt and bullpen coach Ken Howell, a mechanical flaw was spotted in video and League has worked daily on ironing it out.
His last four outings have been scoreless and hitless with six strikeouts and two walks in four innings.
"It's just been a mechanical issue that gets me into position to have more consistency with my fastball, and off the fastball comes the slider and split," League said. "The more I pitch, the more comfortable I'm getting.
"When I'm getting swing-and-misses or foul balls and weak ground balls, that's how I know I'm doing what I'm supposed to be doing."
League's acquisition for Minor Leaguers Leon Landry and Logan Bawcom allowed the Dodgers to trade Josh Lindblom to the Phillies to get Shane Victorino.
"He's been really good," manager Don Mattingly said. "He works really hard, and that's what I like so far. He's throwing a lot more strikes with greater depth. I feel comfortable with him against righties and lefties. His work is paying off."