CHICAGO -- Lucas Giolito and Jack Flaherty met at Guaranteed Rate Field approximately four hours before the White Sox played host to the Cardinals in Monday night’s Interleague series opener.

The duo eventually got together with White Sox pitching coach Ethan Katz for a picture. It was a Harvard-Westlake High School reunion, with Giolito and Flaherty having pitched together in that same rotation, along with Atlanta’s Max Fried, all of whom were coached by Katz. That period in Los Angeles was the precursor to their Major League success, with Giolito, Flaherty and Fried all making Opening Day starts for their clubs during the 2021 season.

But this bond of friendship will take a slightly different turn Tuesday when Giolito and Flaherty take the mound opposite one another as their respective team’s hurler. It’s the first time they will pitch against each other, by their recollection.

“Definitely one day, [we’ve discussed] all being in [the league], all three of us,” Flaherty said. “In terms of matching up, I don't know if that was ever [discussed]. I think it's more of a conversation of Max vs. Lucas, and hopefully that happens at some point. But it’s going to be fun.”

Flaherty knew there was a chance that the two could face off. After his last start Wednesday, he saw that Giolito had thrown the same day in Minnesota, and with both teams having off-days that ensuing Thursday, the rotations for the respective Central division leaders lined up perfectly.

“It was right after my game, my last one, he shot me a text saying, ‘Are you going Tuesday?’” Giolito said. “And I was like, ‘Yup, that's when I'm slated for.’ And then I kind of looked at his schedule, like, ‘Oh, OK! Cool.’ So it was like five days ago.”

“Once it happened, it was like, ‘All right, this would be cool, this would be fun,’” Flaherty said.

And it won’t just be a Flaherty-Giolito reunion Tuesday.

Matt LaCour, the duo’s head coach at Harvard-Westlake, is said to be flying in for the game. Katz has kept a close relationship with Flaherty, and he might be the one character who is able to get Flaherty off balance before the contest starts, as he and Giolito warm up on opposite sides of the outfield grass.

“I'll probably laugh for a split second or whatnot,“ Flaherty smiled. “He's going to try to get me out of what I do. I know he's going to try and talk to me, come out there and see me before the game.”

Will it work?

“Of course not,” Flaherty added.

Meanwhile, Giolito wouldn’t take the bait when asked which one of the three accomplished pitchers was Katz’s favorite.

"Well he did come over to coach over here, so maybe that says something,” Giolito laughed. “I don't think that he has one. Even if he did, he's not going to tell you and I don't know.”

Giolito was an older brother of sorts for Flaherty; the one that welcomed him to the school team, the one that took him from field to field whenever he needed a lift. The White Sox right-hander refers to Flaherty’s mother, Eileen, as “Mama Flare.”

“Absolutely love her, adore her. She was at every single game at high school,” Giolito said. “She'd bring us brownies. They're famous around the Harvard-Westlake parts.

“Same kind of goes for my side, my parents love Jack. We're all so close. I think it's just a very cool moment. It was going to happen eventually between the three of us. We're eventually going to have to line up at some point, and so this is the first time hopefully of very many over the next 10-15 years. It's just going to kind of be a moment for our families and friends and old teammates from our high school days.”

Ultimately, this competition is about winning. Flaherty enters with an 8-0 record, 2.53 ERA and 55 strikeouts over 53 1/3 innings. Giolito is coming off one of his best starts of the season, striking out 11 over eight innings in a 2-1 victory over the Twins, and raising his strikeout total to 61 over 49 2/3 innings.

These staff aces have battled other No. 1 starters in the past. But this contest has a little more of a personal connection.

“We have a very, very strong relationship, and it runs from friendship to teammates and [then] being in pro ball, obviously different organizations,” Giolito said. “Getting together in the offseason, working on things. I've asked him plenty of questions about his slider in the past, he's asked me questions about my changeup. And kind of watching each other, all that kind of stuff. We've been doing that forever.”

“It's going to be a special day, and I know both teams want to present their starting pitcher with a lot of offense and a lot of defense,” White Sox manager Tony La Russa said. “It will be a classic competition. I'm looking forward to it.”