It was unbelievable then, and if you ask Lefferts about it, it's unbelievable now, 30 years to the date: April 25, 1986. In fact, it's part of baseball history.
Lefferts' unlikely long ball marked the first time a pitcher had hit a walk-off homer in the Major Leagues since Jim Hardin of the Orioles did it off Royals pitcher Moe Drabowsky on May 10, 1969.
And it hasn't happened since then.
"It's one of the most special days of my career," said Lefferts, now the Minor League pitching rehab coordinator for the Oakland A's. "It's just doing something that you don't expect to do. It hadn't happened for 17 years before I did it.
"So that's one time in 47 years. That's pretty cool."
Lefferts worked hard for every inning he got in the big leagues. He was a ninth-round Draft pick by the Cubs in 1980 and made it to the Majors in '83 with Chicago. He was traded to the Padres in December of that year. By the time the '86 season rolled around, Lefferts was 28 years old and a dependable left-handed arm out of the bullpen.
Lefferts was not much of a hitter, although he did love to swing the bat.
"It was one of the things I really enjoyed about being in the National League," Lefferts said. "My first 10 years I was a reliever, I'd get like five at-bats a year. We would take [batting practice] every day. I would go up there swinging for the fences every day, so why not? We'd have home-run-hitting contests among the pitchers, but none of us were very polished as far as hitters go.
"I don't think any of us ever dreamed we'd actually hit a homer in a real game."
Until it happened.
Lefferts, who was suffering from a 102-degree fever that Friday night, wasn't even supposed to enter the game against the Giants, but future Hall of Fame closer Rich "Goose" Gossage gave up two runs in the ninth to blow the save. Gossage plowed through a perfect 10th with the score still tied at 7 until it was time for Lefferts. The mustachioed southpaw pitched a scoreless 11th inning, watched as Giants reliever Greg Minton did the same in the bottom of that frame, and then gave up a run in the 12th.
Fortunately, the Padres had Lefferts' back before he had theirs. Graig Nettles homered off Minton to lead off the last of the 12th, tying the game at 8. After a Garry Templeton groundout, Lefferts exited the on-deck circle.
Lefferts knew Minton was good. The veteran right-hander had made an All-Star team and finished sixth in NL Cy Young Award voting four years earlier. He also knew Minton threw a nasty sinker, and he had to be ready for it.
Lefferts did what he always did when it was his time to hit: he grabbed the bat of his teammate, future Hall of Famer Tony Gwynn.
"As a reliever, you don't have your own bat, because it's such a rare instance that you're going to hit," Lefferts says. "Tony always told me I could use his. So I grabbed it off the rack.
"It was a 33 [inch]-31 [ounce] bat. It was light enough that I could swing it."
And swing it he did. The only problem, at least for the first two pitches, was that Lefferts didn't hit much of the ball.
"His sinker was pretty hard to hit," Lefferts said. "I swung and missed at the first one, and then I foul-tipped the second one. At that point, I was just trying to not strike out. I was telling myself, 'You are not going to take strike three.'"
The 0-2 pitch arrived. It was a curveball, and it was a mistake.
"The one thing I will say was that I always swung hard in case I hit it," Lefferts said. "That was my motto. And he was trying to go away, hung one inside, and I was out in front, on my front foot when I hit it."
It was by no means a no-doubter. Lefferts did not stand and admire his work, flip his bat, point skyward or do anything else remotely resembling a game-winning celebration. He put his head down and ran as fast as he could to first base.
"I didn't expect it to happen, so I didn't really walk it off," Lefferts said with a laugh. "I was sprinting around the bases, which was kind of my M.O. anyway. I was almost to second base by the time I knew it was a homer."
Lefferts kept running. He was well past home plate and almost in the dugout by the time his teammates greeted him.
"They play up the home run a lot more nowadays," Lefferts said. "But it was a fun time."
Lefferts was interviewed on the field right after pulling off the stunning feat, and he said he had "a lot of tingles" as he was sprinting around the bases. Not surprisingly, he had no idea that he had carved out his own page of baseball history. But looking back on it now, he said he's pretty sure he won't be the last pitcher to do it.
"It'll happen again," Lefferts said. "But it's still pretty cool."
In the meantime, Lefferts said he's proud of his 12 years in the big leagues and of the work he's doing for the A's, making pitchers better and having a bit of fun with them whenever he gets the chance.
Naturally, there's one topic he can't avoid bringing up.
"I tell all my pitchers that I hit a walk-off home run," Lefferts said.
"Gives them something to shoot for, right?"