For a moment, it appeared ownership partner Magic Johnson would have the honor.
Johnson slowly walked toward the mound with a baseball in his hand as former Dodgers pitcher Orel Hershiser got in position behind the plate. Johnson took a deep breath, looked in at Hershiser and shook off his catcher. Before he could throw the ball, Mattingly hustled out of the dugout and called a meeting on the mound.
Mattingly lifted his left hand and signaled for a lefty.
Koufax appeared from the dugout as the crowd roared and rose to its feet.
"It was pretty cool," Mattingly said after Dodgers beat the Giants, 4-0. "I was kind of working on my acting skills. Pretty weak. I was thinking this wouldn't be a bad lefty to bring in."
Koufax slowly walked toward the mound, first stopping to shake hands with Maury Wills and Tommy Davis from the 1963 championship team and Tommy Lasorda. Johnson greeted him with a hug, as did Hershiser. Mattingly handed Koufax the ball and the pair shared a brief word.
Koufax stood ready at the base of the mound, until Mattingly implored him to step on the rubber.
As music from "The Natural" pumped through Dodger Stadium's new sound system, Koufax kicked off the 2013 season with a pitch that fell just short of the plate.
Koufax shrugged his shoulders, shook Mattingly's hand and then embraced Hershiser once again. As the two walked off the field, Hershiser handed Koufax the ball.
Kershaw followed with a pitching performance that reminded Mattingly of the great Koufax. The lefty shut out the Giants and struck out seven on just 94 pitches.
"I'd be lying if I didn't say it didn't flash through my mind there in about the sixth that this guy is rolling along and Sandy throws out the first pitch today," Mattingly said. "It's probably not fair to Clayton to throw that on him right now. But really for this day, Opening Day and Sandy throwing the first pitch out, just the way Clayton was pitching, it makes you think about him during the game."
Catcher A.J. Ellis wasn't shy about comparing the two left-handers.
"You got a sense on this day, with the first pitch thrown by Sandy Koufax and the last pitch by Clayton Kershaw, it's almost like a passing of the torch today," said Ellis. "He's the most special player I've ever played with."
But Kershaw believes he hasn't quite reached the same level as Koufax.
"I just don't want to disrespect Sandy; he doesn't deserve that," said Kershaw, who put the Dodgers on the board first with a home run to lead off the eighth inning. "He's the best left-handed pitcher ever. Obviously, I'm honored with the comparison. I don't put merit into it. I've got a long way to go."
Austin Laymance is an associate reporter for MLB.com.