(AP Photo/Alex Brandon)

Only the grind of the season will allow Ross Detwiler to prove he can stay healthy. But already, after only one week of workouts, the lefty has proved he is healthy after back surgery last summer, and perhaps stronger than ever.

Detwiler entered spring as the most accomplished starter among those fighting for the fifth rotation spot. His performance early in camp – including the unveiling of a new cutter – has only reinforced his presumed status as a favorite.

“Detwiler is getting stronger every day,” said Livan Hernandez, who once pitched in the same rotation as Detwiler and is now serving as a spring instructor. “Detwiler is ready for this year. I wouldn’t be surprised if he wins a lot of games. I think he’s got the chance to win 15 or more games this year.”

Hernandez sees Detwiler’s fastball “exploding” more than it used to. He also raved about Detwiler’s cutter has looked.

Detwiler has never thrown a cutter before this spring. Coaches had told him the pitch may work especially well with his delivery. He also wanted a different pitch for his repertoire – he threw his fastball 80 percent of the time in 2012 and on 88 percent of his pitches last season.

But when Detwiler had tried to throw a cutter in previous offseasons, it never felt right. For reasons that remain beyond his grasp, throwing a cutter took this winter. In bullpen sessions, Detwiler has remained comfortable — “free and easy,” he said — throwing it.

“I’ve really thrown one pitch,” Detwiler said. “I had a few people tell me it would be good for my arm angle and everything. So I just kind of messed around with it a few times. Finally, this offseason I messed around with it a little bit. It actually felt good.”

Hernandez compared the way Detwiler could use his cutter to Al Leiter, a former teammate. But he thinks Detwiler has better overall control and command than Leiter did.

Like Leiter, Detwiler can use the cutter to jam right-handed hitters and keep them from diving over the plate. It will give him another measure of defense against righties, who have hit .274 against him in his career.

“It just puts something else in the hitters’ minds,” Detwiler said. “I’m not going to try use it too much, do too much with it.”