ATLANTA -- A juke and a missed pitch were the beginning of a downward spiral in the Astros' 6-2 loss in a World Series rematch against the Braves Friday at Truist Park.

In just his second start of the season, Lance McCullers Jr. faced the task of slowing down the defending champs. He came in with an unblemished ERA after tossing six scoreless innings against the Athletics. But after evading danger in the first two innings, the 28-year-old found himself caught in a jam.

After Ronald Acuña Jr. singled, Dansby Swanson hit a tough grounder up the middle that might have become an inning-ending double play. But instead, Jose Altuve dropped a barehanded attempt at second and was unable to tag Acuña, who overran second base, and both runners were safe.

"[That play] set the table [for the home run]," manager Dusty Baker said. "It was determined that it was a hit, so that was a tough play for both of them. [Jeremy Peña] made the right play. Just because you don't get the out, that doesn't mean that it's the wrong play. ... Sometimes that's how the ball bounces, you've heard that saying before, sometimes it doesn't bounce your way."

The official ruling was a single, and McCullers now had to face National League MVP candidate Austin Riley with two on and one out. Riley took advantage of the mistake with a three-run homer to open the scoring.

"Obviously, you'd like a couple things to go different here or there," McCullers said. "Felt like I made some solid pitches and just didn't have the result. And then, a really good hitter took my mistake and hit it a really long way. And that's kind of how this game goes."

While dealing with a dangerous lineup, McCullers also had to pitch through the thought of his teammate's health.

Astros left fielder Yordan Alvarez left the game in the fifth inning after experiencing shortness of breath. The 25-year-old was transported to a local hospital for further evaluation after being evaluated in the training room.

"He still has to see the ER doctor," Baker said in his postgame press conference. "He had shortness of breath. Then when they shot the fireworks off, the smoke made it worse. I'm glad we got him out when we did because I looked up, and he was in the dugout. It was kind of a scary moment because it could be anything. They said that he's doing fine at the moment."

Mauricio Dubón was the defensive substitution, taking over in center field and moving Chas McCormick to left field to replace Alvarez. But an inning later, Dubón would have to exit the game with a left elbow contusion after crashing into the center-field chain-linked fence attempting to catch Swanson's two-run double.

With a lot on his mind, the right-hander understands that there were a lot of things out of his control, and this is only a stepping stone to where he'll be with more outings under his belt.

"This is my second start," McCullers said. "I know we're deep into the season, but it's early for me. I'm still working through stuff, and I'm still trying to get 100%, mechanically speaking."

The 6-foot-1, 202-pounder felt the playoff atmosphere in the first game of the World Series rematch, and even though he didn't have the outcome that he wanted, he's looking forward to the next time that he gets to face the Braves roster, potentially in a more meaningful setting.

"This is a long way from where I'm going to be here in a couple starts, I believe," McCullers said. "They have a good ball club. They're playing well right now. I think if I face them again, and can have my stuff a little bit more sharp, I think I'll have a little more success."