So with Peavy's Padres and Oswalt's Astros set to face each other on Monday at PETCO Park in each club's regular-season opener, the natural assumption is these pitchers just might take it easy on each other when the other is hitting.
Don't count on it.
"It's kind of ironic that we're pitching against each other on Opening Day," Peavy said of his buddy Oswalt. "But I promise you this: He's going to try to do anything to win, and so am I. There are no buddies from 7:05 until the end of the game. After that, we'll be going out to dinner and hanging out."
Peavy and Oswalt first met five years ago at the behest of former teammates Ricky Stone and Scott Linebrink, if for no other reason than the two appeared to have similar interests. From there, the friendship blossomed, as the two hung out at the 2005 All-Star Game in Detroit.
They spent time together each offseason as Peavy is from Alabama and Oswalt is from Mississippi.
Oddly enough, Oswalt isn't big on fraternizing with opposing players and prefers not to be friends with anyone who isn't a teammate. With Peavy, though, it's different.
"We're just a lot of the same. We're from the same part of the country, we enjoy doing the same things and we pitch. We're the same people," Peavy said. "When you meet somebody who is like you and has the same interests, it doesn't take you long to hit it off and become buddies."
Peavy and Oswalt talk by phone often and have an undisclosed bet riding on the game. There was a little trash talking when the two spoke last week when Peavy was in Arizona and Oswalt was in Florida training with the Astros.
On Monday, it will be all business, their friendship put on hold for a few hours.
"It'll get real serious once we cross the lines," Oswalt said. "Maybe there will be a little smile if I hit a bomb off him or he hits a bomb off me. But it'll be all business once we get on the field."
Peavy certainly got the better half of his matchup with Oswalt on Monday, as the defending Cy Young Award winner knocked in the Padres first two runs in a 3-0 victory over the Astros with a hit and a sacrifice fly.
Peavy tossed seven shutout innings while Oswalt allowed three runs on 11 hits over 5 1/3 innings and went 0-for-2 at the plate.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.