PITTSBURGH -- The Blue Jays have made the Pirates’ pitchers work. It makes sense: Toronto is one of the top offensive teams, with top-five numbers league-wide in all slash line categories.

The visitors’ pesky offense once again tried to chip away at Roansy Contreras in one of his biggest tests this season, but the rookie right-hander showed a lot of composure to keep the Pirates afloat in his six innings before Toronto went on to win, 4-1, Saturday at PNC Park.

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Contreras’ first battle came in weird fashion, as he seemingly got out of the first inning by stranding a runner on first with a strikeout of Matt Chapman. But his slider bit so hard away from Chapman that it bounced past catcher Jason Delay and allowed the Blue Jays' hitter to reach and put two on.

In the third, Contreras got his rematch with Chapman with two on, and he completed the strikeout for good. But the fourth inning proved to be his toughest obstacle.

Bo Bichette hit a single and Lourdes Gurriel Jr. doubled to put runners on second and third with no outs, eliminating the hope of a double play. These tend to be the innings where things spiral on a young pitcher, but Contreras gave up one run on a groundout and permitted nothing further.

“Any time in a situation like that, I just try to remain calm,” Contreras said through interpreter Mike Gonzales. “Not try to focus on that stuff, but focus more on just executing my pitches and dominating the hitter.”

A throwing error by Oneil Cruz, who tripled in the Bucs’ lone run, put runners on the corners with one out in Contreras’ final high-leverage spot in the fifth, but he got a strikeout and flyout to escape.

“He was extremely effective,” manager Derek Shelton said. “That's a good lineup. They make you grind. We saw it last night and we saw it tonight, they foul off a ton of pitches. He pitched really well."

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Unfortunately, the same could not be said for Duane Underwood Jr. He replaced Contreras in the seventh, and while he got ahead of all six batters he faced, he converted only two outs.

George Springer (0-1 count to start) singled, Vladimir Guerrero Jr. (1-2) walked and Chapman (1-2) walked. With two outs, Underwood got Bichette to a 1-2 count, but the shortstop, who had already stranded a runner in scoring position twice, worked a 10-pitch at-bat to line a bases-clearing double.

“He's got to execute pitches,” Shelton said. “The Bichette at-bat was a heck of an at-bat by Bichette, but Duane's just got to execute pitches."

Despite the unfortunate ending to the game, Contreras appears to be on pace for a strong final month. He’s going deeper into games than ever; he’s pitched six innings or more four times this season, and those have all come within his past five starts. Though he has good strikeout stuff, Contreras is learning to use the defense for efficiency’s sake, too.

“[I’m] focusing on just throwing less pitches by trying to get ground balls, get some popups, and I feel like that’s what’s been giving me a lot better results,” he said.

This kind of growth has been one of the Pirates’ biggest developments in a season that has not gone their way.

“I think we continue to see him stay calm,” Shelton said, “and that’s just a positive sign of what kind of pitcher he’s going to be.”