PHOENIX -- Justin Steele walked off the mound with both of his arms skyward. The Cubs pitcher was celebrating a dazzling sliding catch in right field by Seiya Suzuki, one that stranded a runner on third base to escape a first-inning jam on Sunday afternoon.

It was the start of a stellar performance for Steele, who racked up a career-high 10 strikeouts to set the tone in a 3-2 win over the D-backs at Chase Field. The left-hander was both efficient and overpowering, looking very much the part of the reliable rotation piece the Cubs have been trying to unlock.

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"He's fun to play behind," Cubs third baseman Patrick Wisdom said. "He just has that kind of persona and that energy about him, that aura. He's intense on the mound, and I love it."

Steele's performance was notable in a few regards:

• Not only did he set a career high with 10 strikeouts, but he became the first Cubs pitcher to have double-digit punchouts since Kyle Hendricks on Sept. 18, 2020.
• Prior to Steele's outing Sunday, the last Cubs lefty with 10 strikeouts in a start was José Quintana on Aug. 13, 2019. 
• Steele became the first Cubs draftee to notch at least 10 strikeouts in a start for the Cubs since Jeff Samardzija did so on May 26, 2014.

"He continued to attack," Cubs manager David Ross said. "It looked like the ball was running all over the place for him. The lefties didn't seem to have a lot of answers for him."

The big question coming into the game for Steele was whether his slider would be effective.

In his last outing on May 8, his left thumb began to swell in the fourth inning against the Dodgers. It became increasingly uncomfortable for Steele to grip that pitch. That seemingly put his next start in jeopardy, but the issue improved over the past week. Steele's bullpen session on Friday convinced the Cubs he was ready to go.

Against Arizona, Steele featured the slider 25 times, generating nine swinging strikes. He had 12 swinging strikes with the pitch in his previous 22 innings this season.

"My slider was working very well," Steele said. "I was able to get it for swing-and-miss and for strikes whenever I wanted. I really felt good with it."

That is Steele's go-to put-away pitch, but Cubs pitching coach Tommy Hottovy has stressed with the lefty that outs on early counts are crucial. The strikeouts will come, but Steele has to create those chase scenarios by first pounding the zone with his four-seamer and sinker.

With that in mind, Hottovy has challenged Steele to end as many at-bats as he can in under four pitches.

"Focus a lot more on, literally, how many guys can we get out in three pitches?" Hottovy said. "We know the swing-and-miss is going to be there. But how can we get early outs? How can we get quicker outs early in the game to kind of prolong that pitch count?

"What's hurt him has not been stuff. It's been long at-bats, long innings and next thing you know, you're in the third or fourth and you have a high pitch count. So being able to manage that has been one of our No. 1 goals."

Overall, Steele ended 11 at-bats in three or fewer pitches. The lefty had 17 of 24 plate appearances in the game conclude by the fourth pitch. He threw 14 or fewer pitches in five of his six frames -- the exception being a 30-pitch fourth.

In that fourth inning, Jordan Luplow opened things by drawing a walk in a 10-pitch battle. Later in the frame, a fielding error by shortstop Ildemaro Vargas led to Steele facing two additional batters. Steele found a way to limit the damage to two runs (one earned).

Going into Sunday, he was averaging 19.4 pitches per inning and had not turned in five innings in an outing since April 9. Even with the lengthy fourth, Steele's pace was 15 pitches per inning against the D-backs.

"It's very important," Steele said of getting outs on early counts. "The starts that have kind of been not quite as good this year for me have been starts where I have a bunch of 3-2 counts, three-ball counts, a bunch of six-, seven-pitch at-bats."

In the first inning, Steele yielded a leadoff triple into the right-field corner to Cooper Hummel. The lefty followed with a trio of three-pitch outs. He struck out Luplow, induced an infield popout from Ketel Marte and then watched Suzuki rob Christian Walker of a hit.

"He usually has like one little bump in the road inning that costs him a lot of pitches," Ross said. "But today, he did a really nice job of just pounding the zone, making those guys earn it."