(Photo by Jason Miller/Getty Images)

Corey Kluber emerged as a legitimate starter last season for the Cleveland Indians, going 11-5 with a 3.85 ERA and 136 strikeouts in 147.1 innings. His Fielding Independent Pitching, which measures what a player’s ERA should have looked like over the season, was 3.36, 30th best among pitchers with at least 100 innings pitched.

This season, the 28-year-old right-hander is in the conversation for the American League Cy Young award. Kluber is 13-6 with 9.8 strikeouts per nine innings in addition to a 5.2 strikeout-to-walk ratio and trails only Seattle ace Felix Hernandez in Tom Tango Cy Young Points, a projection of how the BBWAA will vote at year’s end.

Kluber will tell you that it started with the two-seamer fastball, or sinker.

“I’d never really thrown it much on a consistent basis,” Kluber said. “I’d throw my four-seam and, here and there, I’d mix in a two-seam. After I threw it over and over and over and over, and it kind of clicked. It was like, ‘This feels a lot better.'”

But his curveball is what is driving his success today. Here are the 10 most valuable curves in baseball this season among starters qualifying for the ERA title, according to PITCHf/x run values per 100 pitches.

Hitters are batting .076 against the breaking ball with an isolated power of .032. Of the 12 hits against, just five have gone for extra bases, and all those were doubles.  Lefties (.096 average) and right-handers (.068 average) have been stymied by Kluber’s breaking ball this year.

That’s because Kluber is getting more horizontal and vertical movement on the pitch, which has dropped the contact percentage outside the zone from 41.7 percent to 31.8 percent year over year.

Corey Kluber’s curveball (Source: Fangraphs)

As a result, his strikeout percentage with the curve is 56.8 percent, higher than either 2012 (48.7 percent) or 2013 (40 percent).

“He’s getting an air about him like a Nolan Ryan or a Roger Clemens,” pitching coach Mickey Callaway said. “That’s what I feel like when he’s on the mound. I feel like one of those guys is pitching right now.”