SAN FRANCISCO — Jon Gray’s season of change is almost over. The Rockies’ rookie right-hander is scheduled to make his final start Thursday night against the Giants at AT&T Park.

Gray’s growth is plain to see. From his franchise-record 16-strikeout game against San Diego on Sept 17 to his turning-point victory against the formidable Red Sox on May 26 at Fenway Park, he has emerged as Colorado’s potential ace of the future.

“That’s something that he should aspire to be — a guy who could be considered a legitimate ace,” manager Walt Weiss said Wednesday before the Rockies played the Giants in the second game of the series. “(Gray could be) a guy that’s in that Cy Young conversation, at some point. Johnny’s got that type of talent, but you have to go out and do it for a period of time.”

Gray, 10-9 with a 4.54 ERA, entered the season already possessing a 95 mph fastball, a pitch he can crank up to 98. He also owned a wipe-out pitch — an 88-89 mph slider that cuts like a knife when he commands it properly.

But Gray wanted something more; a pitch that would play mind games with batters and set up his power stuff. So he went into spring training determined to perfect his curveball.

“In spring training, I caught his first bullpen and he threw one and I was like, ‘Wow!’ ” catcher Nick Hundley recalled. “I knew it could be a good pitch, but he had to gain the confidence to use it. He had to be able to use it in games, in different counts and against the best hitters in the world.”

There was some trouble with Gray’s curve during spring training, forcing him to ditch it for a time. But beginning with a start against the Dodgers on April 22, he embraced the pitch. More and more, it became part of his arsenal. After throwing no curveballs in his abbreviated 2015 debut season, he’s thrown it nearly 11 percent of the time in 2016.

“I’ve come to see how much throwing the curve has helped,” said Gray, who will be making his 29th start Thursday. “After I’ve shown a hitter that pitch, I’ve seen that it is so much easier to face the hitter the next time.

“I could tell that guys were not hacking away at my fastball like they had been. The curve has become a big weapon for me. Being able to control it as a two-strike pitch was a big step.”

Gray has a 10.07 strikeout rate per nine innings, trailing only the late Jose Fernandez, Robbie Ray, Max Scherzer, Noah Syndergaard and Madison Bumgarner among National League starters. Gray’s ability to strike out batters is tied to his curveball, a pitch that comes to the plate at 77-78 mph, almost 20 mph slower than his fastball.

“His curveball, giving him that separation and change of pace, has been really good lately,” Hundley said. “Whether it’s buying strikes early in the count or throwing the curve in the dirt as a chase pitch late in the count, Jon’s got a really good feel for it now.”

DJ sits. Second baseman DJ LeMahieu, the National League’s leading hitter with a .349 average, found himself on the bench Wednesday night. Weiss has made no secret of the fact that he will do what he can to get LeMahieu the batting crown, so Weiss decided to sit LeMahieu against Giants right-hander Jeff Samardzija.

“I’m just picking my spots, and against Samardzija, I’m loading up on lefties, too,” Weiss said. “I am also trying to preserve his lead. I’m not going to be shy about it. But there is a way to do it the right way. I will pick my spots here and there and DJ will take care of the rest of it.”

Footnotes. The Rockies entered Wednesday night’s game a season-low 11 games below .500. … As a unit, Rockies pitchers have 1,165 strikeouts this season, the second-most in franchise history behind the 2010 club that had 1,234.

Looking ahead …

Rockies RHP Jon Gray (10-9, 4.54 ERA) at Giants RHP Johnny Cueto, 17-5, 2.79), 8:15 p.m. Thursday, ROOT; 850 AM

Cueto is healthy, apparently, after being scratched from his last start with a strained left groin. If the veteran is on his game, he will help the Giants immensely should they make the playoffs. Over his last four starts, Cueto is 3-0 with a 1.59 ERA, with opposing batters hitting just .204 against him. In three starts against Colorado this season, he’s 2-0 with an 0.77 ERA. Meanwhile, over Jon Gray’s last two games, the right-hander has fanned 26 batters, including a club-record 16 on Sept. 17 vs. San Diego at Coors Field. Gray’s slider is a devastating pitch, and he’s commanding it again after a midseason slump. Gray has faced the Giants only once in his career, allowing one run on seven innings in the Giants’ 2-1, 13-inning victory at AT&T Park on May 7.

Patrick Saunders, The Denver Post

Friday: Brewers RHP Brent Suter (2-1, 2.16 ERA) at Rockies RHP Chad Bettis (13-8, 4.92), 6:10 p.m., ROOT

Saturday: Brewers RHP Wily Peralta (7-11, 5.10) at Rockies LHP Tyler Anderson (5-6, 3.54), 6:10 p.m., ROOT

Sunday: Brewers TBA at Rockies RHP German Marquez (1-1, 6.14), 1:10 p.m., ROOT

Regular season ends