SAN FRANCISCO — Jake Cronenworth awoke Monday, he said the next afternoon, “like I was hung over for the fourth straight day.” The San Diego Padres second baseman describes himself as only an occasional drinker, but in this instance, hyperbole felt appropriate. It had been more than two weeks since he took a 96.5 mph fastball off the chin, but continued starting most games. Finally, after another uncomfortable showing Monday night, he received the first concussion diagnosis of his life.

“I wish we had caught it earlier, but just stemming back from when he got hit in the chin, I think it’s one of those concussions that didn’t present itself right away … and it’s kind of just not gone away,” Padres manager Craig Stammen said. “Yesterday was a bad day.”

Stammen spoke early Tuesday evening following the latest lethargic performance for both Cronenworth and the Padres. It was a new day, as well as an occasion for measured anticipation.

Cronenworth was off to the worst start of his career — and off to the concussion injured list for seven or more days, taking with him the lowest slugging percentage of any qualifying big leaguer. Replacing him in the lineup and at second base was Sung-Mun Song, the South Korean infielder who signed a four-year, $15 million contract in December, reaggravated an offseason oblique injury in March and spent recent weeks posting modest numbers in the hitter-friendly Pacific Coast League ahead of his first big-league at-bat.

“We loved having him in spring training; he brought some energy to our team,” Stammen said. “He’s going to bring energy to our team tonight.”

A few hours later, Stammen looked prescient. Batting ninth in a rearranged lineup, Song supplied two hits, a stolen base and a pair of runs scored in a 10-5 victory over the San Francisco Giants. His two-run, opposite-field double off top starter Logan Webb helped fuel a five-run fourth inning, and the Padres went on to match their season highs in both runs and hits (14) while emerging, at least for a night, from an offensive malaise.

송성문 선수의 메이저리그 첫 안타! pic.twitter.com/p0FrjcUFJj

— San Diego Padres (@Padres) May 6, 2026

Perhaps that funk was to be expected. According to Baseball Reference, the average age of San Diego’s hitters — 30.1 years — is fourth oldest in the majors. Biology and recent seasons suggest that such high-paid position players as Manny Machado (33), Xander Bogaerts (33) and Cronenworth (32) will only continue to decline. Slow or alarming starts from Jackson Merrill (23) and Fernando Tatis Jr. (27) have only magnified the issue.

Song, then, represents an intriguing new variable. By baseball standards, the 29-year-old is not exactly young. But Song did not become a standout performer in the Korea Baseball Organization until 2024, the same year a former Kiwoom Heroes teammate debuted with San Francisco on a record-setting $113 million deal.

“When I played with Song, he was never one of the best players out there,” Giants right fielder Jung Hoo Lee said through interpreter Justin Han. “But after he came here to the major leagues, he put a lot of effort. And I think for Song right now, it’s his prime, for sure. He’s showing really good movement out there.”

Song transformed his body ahead of his breakout season in the KBO, adding muscle while retaining his agility. Still, he arrived stateside with a fraction of Lee’s original fanfare. Scouts questioned, and continue to question, whether he can establish himself as a major-league regular. The sparse history of successful transitions by Korean hitters indicates long odds. Lee, the 2022 KBO MVP, has been a roughly replacement-level player early in his third season with the Giants.

On his recent rehab assignment with Triple-A El Paso, Song played 25 games, homered once and logged an underwhelming .717 on-base plus slugging percentage. He surfaced as a 27th man in the Mexico City Series — the Padres and the Arizona Diamondbacks were allowed to carry an extra player — and made a brief appearance, albeit only as a pinch runner.

Ahead of his true debut, he still characterized his PCL stint as a “great experience.”

“It was definitely time that I needed, because I had an injury in spring camp, and coming back from injury, I had no feel for the game,” Song said through interpreter Juneseo Yi. “Getting reps in Triple A, playing multiple positions, helped me a lot.”

Tuesday night, Song popped out to left field in his first at-bat. Then, as the Padres blitzed Webb an inning later, the newcomer demonstrated the ability to adjust. This time, he made 100.8 mph contact on a one-hopper against the wall in left-center.

“First at-bat, I was late on the cutter, so I was thinking about being more aggressive in the second at-bat,” Song said. “And then, luckily, I got the same cutter in a similar location.”

In the top of the eighth, Song displayed his speed and base-running instincts, collecting an infield single, stealing second base and immediately taking third when Giants catcher Jesus Rodriguez uncorked an errant throw. Five pitches later, Song easily scored on a double by Merrill.

It was a successful, unconventional night for most of the lineup. Merrill, batting leadoff despite his early-season lack of plate discipline, went 3-for-5 with two runs and two RBIs. Miguel Andujar, batting third behind Machado, finished a home run shy of a cycle. Tatis, bumped down to the fifth spot amid his season-opening power outage, mustered an opposite-field double.

And Song, pressed into service after Cronenworth’s diagnosis, delivered in multiple ways.

“You don’t really see a lot of guys have a nice overall debut like that,” Bogaerts said. “Offense, defense, even the stolen base. I mean, that was like icing on the cake.”

The Padres are likely to be cautious with Cronenworth — the infielder plans to see a concussion specialist later this week in San Diego — giving Song an opportunity to stick for a while. He is most comfortable at third base, the position where he spent most of his KBO career, but he and Tatis figure to form an athletic platoon at second. While Cronenworth is sidelined, Song will also serve as the primary backup at shortstop.

At the same time, he could provide an intangible boost inside the clubhouse.

“He’s smiling at all times,” Stammen said. “Smiles are a good thing. Laughter is a good thing. He brings a little energy. And I think just, you know, someone from a different country is curious. The guys are curious about him. They want to get to know him. And he’s a fun guy to be around.

“I think just even having him in the locker room with the guys lightens the mood. And then when he gets a hit, we’re all excited for him getting his first big-league hit, RBI, and having a great game.”

Of course, it was only one game. New challenges will lurk around every corner, on and off the field. Although Song’s contract is modest, the Padres need him to be a positive contributor as a big-league rookie; after a lost 2025 season, 19-year-old catching prospect Ethan Salas has been resurgent at Double A, and Triple-A outfielder Jase Bowen could be a serviceable fourth outfielder, but a depleted farm system otherwise offers little in the way of near-future impact. San Diego will require its offense to do more heavy lifting, particularly because even one or two more pitching injuries could spell catastrophe.

In the meantime, Song already seems to be embracing a foreign country.

“In El Paso, I had Mexican food, and it was not bad,” Song said with a smile. “I like it, so I don’t miss Korean food (too) much.”