CHICAGO -- Paul Skenes found himself in a moment of reflection recently, ahead of his Tuesday start against the Cubs at Wrigley Field. For the first time in his Major League career, he would be pitching in a game in September, which overall is new territory for the Pirates rookie phenom.

"It's not something that guys are used to necessarily, especially the young guys,” Skenes said of playing high-level ball in September. “I was thinking about normally what I'd be doing this time of year is starting fall ball. That's what I'm used to. That's kind of the college schedule. So it's definitely something to get used to.”

Tuesday not only was Skenes’ first career start in September in the Major Leagues, but just his second as a professional (he threw two innings for Double-A Altoona on Sept. 1 last year). After a shaky first two innings against Chicago - in which he escaped bases-loaded jams twice -- the big right-hander settled down to throw five scoreless innings, in the Pirates’ 5-0 win over the Cubs.

Skenes walked four, tying his career high, and allowed four hits while striking out six.

"That was a tough one,” Skenes said of the outing. “They made me work in the first one. Made me work a little bit last time, too. It's kind of what they do.”

For as much as Chicago made him work, the outing is perhaps a prime example of the value the Pirates see in Skenes finishing out this season. Pittsburgh manager Derek Shelton reaffirmed on Tuesday the Pirates have no immediate plans to shut down Skenes. The 22-year-old pitching down the stretch is valuable experience both mentally and physically.

And outings such as Tuesday’s are opportunities for Skenes, who has had a stellar rookie season, to continue to grow as a Major League pitcher.

“I think any situation he has like that is just going to make him better,” Shelton said of Skenes’ outing. “Like we've talked about numerous times, a lot of people go through this in the Minor Leagues, and he's going through it at the Major League level. He's going through it at the Major League level in September, and it's a learning experience.”

Skenes’ pitch count was at 54 through two innings, his highest through two innings of any start this season. (Previous: 43 on Wednesday, against the Cubs). He was not landing his breaking stuff consistently, which he attributed to poor execution.

It led to Skenes leaning more on his changeup, and he threw it more than any other start this season (19 percent of the time). His previous high was 10.4 percent on June 17 against the Reds. But Skenes only threw 10 changeups in that outing, compared to 19 on Tuesday.

Skenes threw his four-seamer 46 percent of the time. He threw his splinker 14 percent, his lowest in a start in his career. His previous low for that pitch was 17.3 percent on July 23 against the Cardinals.

"It's a pitch that I've been comfortable with since I was in high school,” Skenes said of the changeup. “I had the opportunity to use it today and had to use it today. I had to reach into the bag of tricks a little bit, but it worked out."

It was perhaps fitting, then, that Skenes made history with his changeup in the fourth inning. He struck out Cubs first baseman Michael Busch on an 87 mph offering below the strike zone to end the inning,

With that strikeout, Skenes tied Cy Blanton's franchise record for most K's by a rookie in a season since 1900 (142), set in 1935.

“He just has four good pitches that he controls pretty well,” Busch said. “I think tonight he went to that changeup a little more instead of the splitter that he’s been throwing. He’s a good pitcher. I thought we had some good at-bats and some chances to drive in a couple runs, and we just didn’t execute."

Skenes has a 2.13 ERA in 19 starts this season. He has gotten five days of rest between each of his starts since the All-Star break. If that trend holds, he is in line to make four more starts this season.

"That's one of the biggest things about this year is just finishing the year and making all my starts, that kind of thing,” Skenes said. “It's definitely a win just to get used to playing through the season. It's going to set me up so much better for next season.”