When Ryan Borucki steps on the mound for the Blue Jays' pre-season opener on Saturday afternoon, it will mark the beginning of his audition for Toronto's fifth rotation spot.

He knows it. And he's fine with it.

"I didn't come in here thinking I had a pencilled in spot or anything like that," the 24-year-old left-hander said at Toronto's spring training facility in Florida last week. "I feel like I still have to prove myself and prove that I can pitch in the big leagues this year and help this team win.

"That's my mindset."

Borucki demonstrated his potential in his rookie season last year, pitching to a 4-6 record and a 3.87 earned-run average over 17 starts after making his MLB debut in late June.

Despite the solid performance -- and despite Toronto's perceived lack of pitching depth at the major league level -- general manager Ross Atkins told reporters in his first spring training media session last week that Borucki was not guaranteed a spot in the Blue Jays' 2019 rotation.

Atkins listed Marcus Stroman, Aaron Sanchez and newcomers Clayton Richard and Matt Shoemaker as the "likely" members of the starting five, providing they stay healthy, and noted that the young Borucki would be competing for the open fifth spot.

Borucki wasn't fazed by that revelation.

"I'm not going in feeling comfortable with my spot whatsoever, and I'm OK with that," he said. "I love competing and I'm excited to get started and show off what I can do."

Borucki is scheduled to start Toronto's exhibition opener against the Detroit Tigers at Dunedin Stadium.

New manager Charlie Montoyo told reporters in Florida this week that he had been impressed with what he'd seen from Borucki -- and some of his other young pitchers -- so far in camp.

"He looked good," Montoyo said after watching Borucki's throwing session Wednesday. "(Elvis) Luciano looked good, (Thomas) Pannone looked good. Everybody was throwing strikes. ... It's a lot of competition, it's a lot of guys, so it's going to be tough."

Borucki lost his MLB debut last June against the then-defending World Series champion Houston Astros, despite a six-inning start in which he allowed just two runs. He was then saddled with four no-decisions and another unlucky loss before picking up his first major league win against the Seattle Mariners on Aug. 3.

While Borucki was content with his first MLB season overall, he was more pleased with the way he rebounded from a tough stretch in late August, turning things around and pitching late into September for the first time.

"When I got to September I could feel my body getting more and more tired," he said. "It definitely was a grind but I got through it and afterwards I realized, 'OK now I have to train my body to get to September.' Before that we always ended (the minor league season) earlier and I didn't have to go that extra month.

"So in that sense last year definitely that was a bit of a wake-up call for me."

The Illinois native, who grew up idolizing workhorse left-hander Mark Buehrle with the Chicago White Sox, said his goal is to pitch 200 innings this year, just as Buehrle routinely did.

Borucki spent the off-season in Toronto, living with his Canadian girlfriend and working out with some other local players at Rogers Centre. He said his off-season goal was to build up strength in order to sustain the rigours of a longer season and he feels good both physically and mentally heading into 2019.

"I finished strong last year and that was the big thing that I took away from (2018)," he said. "I built that confidence going into this year and hopefully from Day 1 when I step on the mound in spring training I'll be able to keep going with that."