Hyun-Jin Ryu’s 34th pitch Monday night at Busch Stadium produced the result he wanted. Miles Mikolas, his counterpart on the St. Louis Cardinals, took the changeup for a called strike to begin the at-bat with two outs in the bottom of the second inning. But the sequence didn’t look right. Ryu didn’t finish his delivery with authority. He was hurt.

Within moments, after Ryu expressed clear discomfort walking around the mound, Dodgers manager Dave Roberts, head trainer Neil Rampe, and the team’s infielders circled their opening day starter. Ryu’s night ended there with a strained left groin -- the same groin he tore off the bone and spent three months nursing last season -- and with the score tied after getting five outs, leaving the Dodgers’ bullpen to secure the final 22 if the team was to extend its winning streak to six games against its most formidable opponent so far this season.

Dylan Floro and Scott Alexander combined to retire 10 straight batters upon Ryu’s absence, but the effort was foiled in the sixth inning when Joe Kelly blew another lead and the Dodgers’ offense, so explosive for the season’s first 10 games, didn’t muster a response in a 4-3 loss to the Cardinals.

After the defeat, Ryu emphasized his early exit was precautionary. He maintained the pain he endured when he tore his groin last season dwarfed the discomfort he felt Monday, which surfaced with his final pitch. But Roberts announced Ryu will be placed on the 10-day injured list and the Dodgers will call up a reliever from the minors to replace him Tuesday. Whether he undergoes a magnetic resonance imaging exam depends on the level of pain he feels in the morning.


“I don’t feel like I’m in a bad place right now,” Ryu said through an interpreter.

The Dodgers (8-3) entered Monday having not trailed since the sixth inning against the San Francisco Giants last Wednesday. But Monday brought a stiffer test, their first meeting with a presumed playoff contender outside the projected weak National League West. They immediately put themselves in position to avoid a deficit again. Four batters into the game, they held a 2-0 lead against right-hander Mikolas. Joc Pederson sparked the ambush by getting hit by a pitch to lead off the game. Corey Seager singled before Cody Bellinger’s fielder’s choice groundout scored Pederson. A.J. Pollock smacked a double down the left-field line to score Bellinger.

The Cardinals’ response was prompt -- and aided by the Dodgers’ defense. After Ryu issued a one-out walk to Paul Goldschmidt, he got Jose Martinez to hit a routine groundball to Seager that should’ve been turned into a double play. But the shortstop’s throw to second baseman Enrique Hernandez was off target, keeping Hernandez from making the turn at second base. Three pitches later, Marcell Ozuna tucked a 115.2-mph line drive inside the left-field foul pole for a two-run home run.

Los Angeles reclaimed the lead in the fifth inning thanks, in part, to Mikolas plunking two more Dodgers. Seager capitalized on the blunders with a one-out single that scored Russell Martin from second base.


While their bullpen kept the Cardinals (5-5) off the board, the Dodgers threatened again in the sixth inning against Mikolas, only to have Hernandez commit another mental blunder. On Sunday, Hernandez’s gaffe occurred in the field, when he didn’t make the turn at second base in what should’ve been an inning-ending double play with one out against the Colorado Rockies.

Instead, he began trotting off the field believing he secured the third out at second base and the Rockies scored. On Monday, he was at second base after doubling when Martin hit a fly ball to shallow center field with one out. Hernandez, thinking Harrison Bader didn’t have a chance to catch it, sprinted to third without hesitation. A charging Bader caught the ball and doubled him off at second base to end the inning.

“I [messed] up,” Hernandez said.

Unlike his mistake in Sunday’s blowout win, Hernandez’s head-scratching gaffe Monday wasn’t an inconsequential humorous detail. The Dodgers didn’t put a runner in scoring position again as they collected a season-low five hits and had just three after the first inning. They had their franchise-record home run streak to start the season snapped at 10 games and were held to less than four runs for the second time this season after beginning the night averaging over eight per game.


Instead of the Dodgers potentially padding their lead, the Cardinals seized it in the bottom of the inning with two runs. The rally began with Scott Alexander, who had tossed a perfect fifth inning, yielding a leadoff single to Matt Carpenter. Roberts said he wanted to avoid using Kelly after he threw 27 pitches Sunday night in Colorado, but Kelly volunteered an inning so Roberts replaced Alexander with him. The move stoked the fire. Kelly walked Paul Goldschmidt and surrendered a game-tying single to Jose Martinez. The right-hander later uncorked a wild pitch that allowed Goldschmidt to score and put St. Louis ahead. Kelly has been charged with nine runs in five innings this season. He has blown the lead in each of the Dodgers’ three losses. His Dodgers career has begun with an inauspicious introduction.

“Joe’s going to keep fighting,” Roberts said. “I believe in him. I know it’s going to turn and I just love the way this guy wants to pitch.”

For the first time in nearly a week, the Dodgers trailed. And for the first time in nearly a week, they suffered a defeat. But the greater loss might have occurred a couple of hours earlier, with their starting pitcher gingerly walking off the field with another groin injury.

The Dodgers already had left-handed starters Clayton Kershaw and Rich Hill on the 10-day injured list. Roberts said immediately replacing Ryu with Kershaw and having him pitch for the Dodgers on Tuesday instead of making his scheduled rehab start for double-A Tulsa was considered, but Kershaw will proceed with the original plan. He is expected to make his season debut as early as Sunday. But he was supposed to join the rotation as a supplement to bolster a unit that has not regularly pitched deep into games, not as a replacement for Ryu, the team’s best starter so far this season.


It’s another setback the Dodgers will have to overcome.

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jorge.castillo@latimes.com

Twitter: @jorgecastillo