On July 2, 1963, two baseball legends engaged in one of the greatest pitchers' duels in baseball history.

Juan Marichal vs. Warren Spahn. Hall of Famer vs. Hall of Famer at Candlestick Park.

By the time Marichal and Spahn met on the mound that Tuesday night, they'd already faced off five times in the Major Leagues. But none of those contests were anything like this.

This was a 16-inning thriller in San Francisco, scoreless until the very end, and both Marichal and Spahn went the distance. It is still the last Major League Baseball game where both starters pitched into the 16th inning.

In the end, Marichal's Giants were victorious over Spahn's Milwaukee Braves, 1-0, thanks to the great Willie Mays' walk-off home run off Spahn in the bottom of the 16th inning.

When it was all over, Hank Aaron, on the losing side, called the game the greatest pitching display he'd ever seen.

But let's start at the beginning.

***

The first time Marichal and Spahn pitched against each other, July 28, 1960, it was only Marichal's third career start. The 22-year-old rookie right-hander was facing one of the greatest southpaws of all time in Spahn, who, at 39, was a 12-time All-Star and the 1957 Cy Young Award winner.

But Marichal gave the baseball world a glimpse of his own Hall of Fame talent. He outpitched Spahn into extra innings -- just like he would nearly three years later -- as the Giants won, 3-2, on Felipe Alou's bases-loaded, walk-off single in the 10th.

In fact, Marichal always seemed to be at the top of his game against Spahn and the Braves. He won each of their first four meetings, and though Spahn finally beat him in their first matchup of 1963, Marichal had never allowed more than two runs when pitching against Spahn in the five games leading up to their all-time classic, with a 1.40 ERA in those games.

On top of all that, by the 1963 season, Marichal was entering his prime. He'd just been named an All-Star for the first time the year before, and that season the 25-year-old would lead the Major Leagues with 25 wins and 321 1/3 innings pitched for San Francisco, while posting a 2.41 ERA and recording a career-high 248 strikeouts.

Spahn, meanwhile, was in the last great season of his career. At 42 years old, the left-hander would earn his 17th and final All-Star nod in '63, winning 23 games himself with a 2.60 ERA and pitching an MLB-high 22 complete games.

Going into their clash on July 2, Marichal was 12-3 with a 2.38 ERA; Spahn was 11-3 with a 3.12 ERA. Marichal had thrown a no-hitter four starts earlier on June 15 … but Spahn had no-hit the same Giants team he was about to face a couple of seasons earlier, on April 28, 1961.

So though there was a 17-year age gap between Marichal and Spahn at the time, their performance on the mound was just about equal. And so it was in their epic duel in San Francisco.

***

If you didn't see the names of the pitchers, you might have expected a slugfest between the Braves and Giants.

San Francisco's lineup had a trio of Hall of Famers in the heart of the order in Mays, Willie McCovey and Orlando Cepeda, plus Alou in the cleanup spot between them. Milwaukee had a Hall of Fame duo of its own, with home run king Hank Aaron and Eddie Mathews batting back-to-back in the lineup, third and fourth.

But, as the baseball wisdom goes, good pitching beats good hitting every time.

Marichal threw the first pitch of the night to Lee Maye in front of 15,921 fans a little after 8 p.m. Over four hours later, as the clock ticked past midnight, not a single run had crossed the plate.

For 15 innings, Spahn and Marichal kept the game scoreless. Marichal baffled the Braves, collecting 10 strikeouts, including two of Mathews and one of Aaron. But the 19-year veteran Spahn matched his younger counterpart inning after inning.

"Here is a guy 42 years old who still has a fast­ball," said Hall of Fame pitcher Carl Hubbell, who was in attendance that night, as he was the Giants' director of player development at the time. "He ought to will his body to medical science."

Neither pitcher gave an inch, and neither would come off the mound while the other was still on it.

Giants manager Alvin Dark tried to take out Marichal at least three times, in the ninth, the 12th and the 15th. Marichal pointed to Spahn and said: "Do you see that man pitching on the other side? He's 42 and I'm 25, and you can't take me out until that man is not pitching."

Spahn kept pitching. So Marichal kept pitching. In the 16th, he got through Aaron and the heart of the Milwaukee order one final time. As he left the mound, he waited for Mays to jog in from center field.

Marichal -- as he recalled in an interview with The Mercury News on the 50th anniversary of the game -- confided in Mays that Dark wasn't going to let him keep pitching anymore.

Mays patted Marichal on the back and said: "Don’t worry. I'm going to win this game for you."

He stepped into the box. Spahn threw him a hanging screwball. And the Say Hey Kid crushed a long drive down the left-field line at Candlestick, into the night and gone. Just like that, one of the greatest games ever pitched was over. It was 12:31 a.m.

"When I saw the ball leave that park," Marichal said, "I was the happiest guy on earth."

***

Such a duel is unheard of in today's game. No pitcher has thrown 15 innings in a game in nearly 50 years, since Gaylord Perry did it on April 17, 1974. No one has even thrown 10 innings in a game in over a decade, since Cliff Lee on April 18, 2012.

Somehow, it was the third time in Spahn's career that he had pitched at least 15 innings, as many times as any pitcher in the Live Ball Era. Marichal had never done so, and would never do so again.

The next day, the headline in the San Francisco Chronicle was simple: "Juan Beats Spahn."

Spahn threw 201 pitches in his losing effort. Marichal threw 227 to beat him.

"I've been around a long time and that's the finest exhibition of throwing I've ever seen," Aaron said. "It may be 10 years or even 20 before you see another its equal."