The actor and late-night host attended Sunday's game between the Boston Red Sox and Los Angeles Dodgers. Despite their long "feud," the two sat next to each another.
Their shirts read: "I'M WITH STUPID" with an arrow pointing at one another.
The stars were rooting for opposing teams. Kimmel, a die hard Dodgers fan, with Boston native Damon cheering for the Red Sox, alongside pal Ben Affleck, who was also in attendance.
Related: Jimmy Kimmel really enjoyed dissing Matt Damon at the Oscars
Damon and Kimmel have had an ongoing battle for the last 12 years, continually seeming to out do themselves with hilarious fake fights and skits on Kimmel's show.
Kimmel took things up a notch when he hosted the Oscars last year, poking fun at Damon for passing up a role in "Manchester By The Sea."
"He handed what turned out to be an Oscar-caliber role over to his friend and made a Chinese ponytail movie instead," Kimmel said on stage. "And that movie, 'The Great Wall,' went on to lose 80 million dollars. Smooth move, dumba**."
It appears this feud is still far from over.
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