PHILADELPHIA -- San Francisco Giants right-hander Matt Cain should have been buoyed after homering in Saturday's third inning. Instead, he felt an odd sense of foreboding as his Philadelphia Phillies counterpart, Cole Hamels, stepped to the plate.

"I'm thinking that he's probably going to try himself to do the same thing, because when you give up a home run to the pitcher, it's probably the most frustrating thing you can do," Cain said.

In fact, Cain had little time to celebrate hitting his sixth career homer. Because with one out in the Phillies' half of the third, Hamels hit his first -- a drive into the right-field seats that traveled an estimated 384 feet.

Hamels, who entered the game batting a creditable .263, insisted that he wasn't trying to hit for the distance.

"No. No," he said. "Every time I get up there, I'm just trying to hit the ball. I'm just glad I hit it further than right at somebody and eventually you get credited with a homer."

Giants manager Bruce Bochy thought otherwise.

"It looked like Hamels was determined to get even with him, and he crushed it," Bochy said.

The rest of the game, which resulted in a 6-5, 10-inning victory for the Giants, was extremely eventful. Yet nothing else that developed during the three-hour, 12-minute contnest at Citizens Bank Park aroused as much curiosity as the rarity of two starting pitchers homering off each other in the same inning.

It marked the first time that starting pitchers had homered off each other since May 18, 2002, when Atlanta's Kevin Millwood and Colorado's Denny Stark did so at Coors Field. No pair of starters had gone deep against each other in the same inning since May 14, 1990, at Dodger Stadium, when Montreal's Kevin Gross and Los Angeles' Fernando Valenzuela slugged it out.

The Cain-Hamels double-pump unearthed a slew of factoids:

• Opposing pitchers hadn't homered in the same inning since April 13, 1997, when Montreal's Carlos Perez went deep against Colorado's Kevin Ritz and Rockies reliever Darren Holmes homered off Perez in the fifth.

• A Giants pitcher and his opposite number last homered in the same game on June 13, 1988, at San Diego, where Mike Krukow victimized Padres starter Eric Show in the third inning before Mark Davis homered off Giants reliever Don Robinson in the eighth.

• The last Phillies pitcher to hit a homer and allow one to a pitcher in the same game was Johnny Couch against Cincinnati's Dolf Luque on Aug. 18, 1925.

• According to records available since 1919, never in Giants history had both starters homered in the same game.

Told that Hamels had never homered before, Cain said, "I don't know that it's any better to know that's the first one."

Moreover, Hamels hadn't yielded a homer to a pitcher in his seven-year career until Cain struck. But Hamels took comfort in his own homer.

"It was nice. You wait long enough and hopefully, eventually, you can have one," Hamels said. "The situation that it happened, I think that I'll enjoy that more than anything with giving up the first home run I've ever given up to a pitcher, to be able to get one.

"Most of the times when you hit a home run, you're supposed to win those games. I guess because I gave up one to Matt and I ended up getting one, I guess it's good that we broke with a tie."

The quality of the principals added to the event's improbability. Cain entered the game with a 2.56 ERA, fifth-best in the National League, and ranked third in opponents' batting average (.210). Cain and Hamels both ranked among the league's top 10 in winning percentage, innings and strikeouts. Both were named NL All-Stars for the third time earlier this month.

Interestingly, Cain (eight innings, five hits, five runs, two walks, four strikeouts) and Hamels (7 2/3 innings, 10 hits, five runs, three walks, six strikeouts) emerged with similar pitching lines.

"I think we're just the opposite twins right there, him from the right side, me from the left side," Hamels said. "I guess we were separated at birth. Every time we pitch against each other, they're tough games and it can go either way. I think that's pretty ironic just to kind of see the way that happened today. I'm sure we'll be talking about it later."