Adbert Alzolay had the best start of his big league career on Saturday, but his night ended with a thud.

Following a two-out triple for Edmundo Sosa in the fifth inning, Alzolay threw an 0-1 slider to Lane Thomas that caught too much of the plate. Thomas drove the ball to center field, scoring Sosa and tying the game. Two innings later, Alzolay once again caught too much of the plate on a hanging slider to Yadier Molina, and the 18th-year catcher shot it out to left field for the go-ahead home run as the Cubs fell, 2-1, to the Cardinals.

• Box score

But despite taking his fourth loss of the season, Alzolay said this game was a huge step forward for him as a starting pitcher.

Alzolay got through seven innings for the first time in his career, didn’t walk a batter for his third straight start and threw 70 of his 86 pitches for strikes. He didn’t get much support from the lineup, as Cubs hitters recorded just three hits after the first inning, but Alzolay’s best start in his first game at Busch Stadium gave Chicago more than a chance to win.

“Overall, to be honest, I felt that today was my best game so far,” Alzolay said. “I was completely in control over all my pitches. Even in the seventh after the homer, I feel that even my emotions were where they were supposed to be. Keep attacking the guys, getting those ground balls there. I feel that overall, I take this game as a really good one for me moving forward.”

The third-year starter retired the first 10 Cardinals batters he faced Saturday -- the furthest he’s gotten into a game without allowing a baserunner -- with five of the at-bats ending in a slider, the pitch that’s become his staple in 2021.

Heading into the game, Alzolay had thrown sliders on 45.9 percent of his pitches. According to Statcast, that was the third-highest rate for a breaking ball or an offspeed pitch by a starting pitcher (on a minimum of 200 pitches) this season. It’s become the go-to pitch for him after curveballs and fastballs took up 33.1 and 31.5 percent of his pitches, respectively, in 2020.

Alzolay took that to another level against St. Louis, throwing sliders on 47 of his 86 pitches and getting whiffs on eight of the 28 swings Cardinals hitters took on the pitch. That control helped fool batters when he added his sinker and fastball to the mix, which he threw for 36 of his other 39 pitches on the night.

“You tell him nice job. I mean, 'Way to throw the ball' were my words,” Cubs manager David Ross said. “I thought he threw the ball great. I think there's some learning experiences in that outing that he'll take away, continue to grow from that. But [it was a] spectacular outing from him. Just came up a little short.

“Really, a couple bad pitches in a really nice night for him. Sometimes that's how it goes in the big leagues. You can pitch really well and still lose, but I thought that was a really nice outing from him.”

Alzolay started his night with a 1-0 lead thanks to an RBI single from Javier Báez in the top of the first, but with no offensive success for the Cubs after that inning, he didn’t have much room for error with the slider.

When Alzolay finally did miss, the Cardinals made him pay. Both of St. Louis’ runs and three of the five hits he allowed came on the pitch, capped off by Molina’s go-ahead shot in the seventh.

“He looked good,” first baseman Anthony Rizzo said. “After a big game last night for us, he comes out and sets the tone for us. … He pitched well for us. These are usually the type of games that are played here, us versus the Cardinals, and they came out on top today.”

For a pitcher with just 14 starts in the Majors, a few misses aren’t surprising. But Alzolay took everything in stride. He said he felt confident in every pitch he threw, and even in the loss, was upbeat about his performance.