CHICAGO -- Chicago Cubs rookie starter Shota Imanaga lowered his ERA on the season to 0.84 on Saturday after throwing seven shutout innings in his club's 1-0 victory over the Pittsburgh Pirates.

It's the lowest mark through a pitcher's first nine career games since ERA became an official stat in 1913, besting Fernando Valenzuela, who compiled a 0.91 ERA after nine starts in 1981.

"If I'm being honest, I'm not really too interested in my own stats or any historic value," Imanaga said after the game through the team interpreter. "But just knowing that there are so many good pitchers that came before me is a good learning experience."

Imanaga, 30, gave up four hits while striking out seven including his final batter with two on and two out in the seventh inning. He used a combination of nearly all fastballs and splitters to stymie the Pirates, making him the very early front-runner for NL Cy Young. Pirates manager Derek Shelton was asked why he's so tough to square up.

"That's a great question," he answered. "This guy is going to give hitting coaches nightmares. The fastball is not 94-95 mph but it's effective. The split is real. It's strike to ball."

Imanaga averaged just 90.9 mph on his fastball, which he threw 46 times. The rest of his pitches were splitters -- save four curveballs. All of it was extremely effective, moving from the top of the zone with the fastball and coming down with his split.

"You feel the hitter a little in-between," Cubs manager Craig Counsell said. "It makes both pitches better."

The Cubs won the game on a walk-off RBI single by Christopher Morel that plated Cody Bellinger, though the play at the plate was reviewed before the celebration at Wrigley Field could begin. It's the team's first 1-0, walk-off win since September 2015.

"We've won two 1-0 games that he's started," Counsell said. "It's hard to win 1-0, and the fact that he's been the starter nine games into his career in two of them is incredible."

In addition to being the lowest to start a career through nine outings, Imanaga's 0.84 ERA is also the third lowest through the first nine games of a season for any pitcher, trailing only Jacob deGrom (0.62) in 2021 and Zack Greinke (0.82) in 2009. The win came a day after Pirates rookie Paul Skenes struck out the first seven batters he faced en route to a six-inning, no-hit performance. Imanaga did him one inning better, making the Pirates the ninth different team unable to solve the lefty.

"We're fortunate to watch it," Counsell stated. "His aptitude, pitch-making ability, his stuff, his competitiveness. They've all been a joy to watch."