After a strong but somewhat uneven debut last year, Yu Darvish has emerged as the bona fide ace Nolan Ryan thought he was getting when he invested $112 million in the Japanese pitching phenom. Hailed as a preseason Cy Young favorite, Yu Darvish is building the foundation for his case with a stellar start to his sophomore campaign.Since coming within one out of a perfect game in his first start of the season, Darvish has been one of the best pitchers in baseball. The 26-year-old flamethrower currently leads the majors in strikeouts 111 and K/9 rate 12.3. He also sports a 2.77 ERA, 0.93 WHIP and 4.63 K/BB ratio while limiting opponents to a .181 batting average. At the rate he’s going, he could punch out 300 batters by season’s end, which hasn’t happened since Randy Johnson passed the benchmark in 2002. What’s more, 300 Ks would put him in the same club as immortal hurlers Bob Feller, Sandy Koufax and Pedro Martinez.Yu Darvish has boosted his already-elite strikeout rate by making a key adjustment in his approach. Rather than trying to blow everyone away with his blazing fastball, as he seemed to do last year, he’s relying less on his heater. Instead, he’s going to his slider more than twice as often as he did last year, a wise decision given that his slider is regarded as the best in the business. Consequently, Darvish is getting more swinging strikes and weaker contact than he did last year. He’s keeping batters off-balance and on their toes instead of letting them sit on his fastball.Another driving force behind Yu Darvish’s breakout is polished command. He’s getting more first strikes, which allows him to get in the driver’s seat and dictate how each at-bat plays out. Whereas he issued 89 free passes last season — fourth most in the American League — and posted a 4.2 BB/9 rate, he’s trimmed his walk rate to 2.7 batters per nine innings in 2013. This improvement has helped him become more efficient with his pitches and last deeper into ballgames, as he’s completed at least six innings in all but one of his 12 starts this season. No wonder the Rangers have won 75 percent of his starts.