CHICAGO -- In a span of five plate appearances on Tuesday night, during an evening that the Cubs' lineup spit on an exhausting number of pitches, Ian Happ embodied the team's offensive approach to date this season.

In a cameo as Chicago's leadoff man during a 6-3 victory over the Cardinals, Happ reached base four times, walking twice, launching a home run and chewing his way through 23 pitches. It was a relentless effort while filling in at the top of the order while Kris Bryant is sidelined with a left wrist issue.

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"Ian, wherever I put him, it doesn't matter," Cubs manager David Ross said. "I think he's as locked in with what he's trying to do at the plate and who he is than I've seen him."

With the win, the National League Central-leading Cubs improved to 15-7 and took a 2-1 lead in this five-game, three-day series against their rivals. The victory went to Yu Darvish, who worked six solid frames and was supported by a marathon effort by the North Side nine.

Entering the night, the Cubs led the Majors with 4.25 pitches per plate appearance, and that was in full effect against St. Louis. In eight innings, Chicago's lineup saw 207 pitches, or an average of 5.05 per PA. The Cubs saw between 22-40 pitches in each frame from the second to seventh.

"It's going to pay off at some point," Ross said. "They don't give in. They continue to take their walks, grind at-bats, look for their pitch, have their at-bat. Super relentless lineup. One through nine, these guys just continue to do that."

The Cubs drew eight walks and had at least one runner aboard in each inning with the exception of the eighth. Chicago did leave the bases loaded twice, but the Cubs had a two-run showing in the seventh -- powered by an RBI double from Victor Caratini and a sacrifice fly by Jason Kipnis -- that helped them pull away.

Jason Heyward followed a leadoff walk by Willson Contreras in the fourth with an RBI triple.

One frame later, Javier Báez led off with a double that landed at the base of the bricks and ivy in left-center. The shortstop then stopped in his tracks and stared in awe at the two-run homer Kyle Schwarber slugged to the right-field bleachers.

"Top to bottom, I think that's kind of what we want it to look like," Happ said of the lineup's showing. "Those runs at the end of games, that's what we need to keep doing."

Happ led off the first inning with a single, and then he slashed a 1-1 pitch from Daniel Ponce de Leon over the wall in left-center for a solo shot in the third inning. In the fourth, the Cubs’ center fielder struck out looking on an inside offering with the bases loaded in an at-bat that ate at him after the win.

"Those are the ones that you look back on and you go, 'I need to be better,'" Happ said. "I need to put the ball in play there. I need to give us a chance to score a run."

Happ later added walks in the sixth and seventh innings.

"Being able to work the 3-2 counts and get on base for Rizz [Anthony Rizzo]," he said, "I mean, that's what I want to keep doing."

Usually, Bryant is in the leadoff spot ahead of Rizzo, but the star third baseman is out until at least Friday after having a medical injection in his ailing left wrist. That created the opening for Happ, who has steadily worked his way up the order this year.

On Opening Day, Happ was in the ninth slot. He homered. On Aug. 9, Ross declared that Happ was "the real deal" and had earned the everyday job in center. Happ reached base three times in the next game. And now, as Bryant's temporary replacement at the top, Happ was the ideal table-setter.

With his performance, Happ improved his slash line to .313/.439/.627 through 22 games played. He has also posted a 183 wRC+, meaning Happ has performed 83 percent above average offensively.

In a way, Happ has represented the kind of offensive look that Ross has preached for his lineup.

The manager has emphasized not making contact simply for the sake of making contact, and really valuing seeing pitches and drawing walks, even if that means a spike in strikeout rate. Going into Tuesday, the Cubs had the highest strikeout rate (28 percent) in MLB, but they were drawing walks at an 11.3 percent clip.

Happ entered the night with a 27.7 percent strikeout rate, 16.9 percent walk rate and was seeing 4.35 pitches per PA. The strikeouts have not hindered the patience or production.

"I want these guys to be themselves," Ross said. "Have a plan and stick with their plan, no matter the situation. I think that's the thing that I want to stress."