The Yankee slugger and the sexy actress were all over Cabo San Lucas, Mexico, over the weekend, enjoying the fun and sun with A-Rod's two little daughters.
The on-again, off-again -- now back on-again -- couple looked cozier than ever.
Diaz looked particularly comfortable cradling her boyfriend's daughter Natasha, 6.
The little girl and her sister, Ella, 2, are Rodriguez's daughters with ex-wife Cynthia Scurtis, who divorced the Bronx Bomber in 2008.
The 35-year-old Yankee third baseman dated "Almost Famous" actress Kate Hudson through much of the Bombers' 2009 run to a world title.
Many Yankee fans credited Hudson's calming influence on A-Rod for his uncharacteristically clutch postseason performance during the 2009 playoffs.
After breaking up with Hudson, A-Rod began dating Diaz in the middle of this year's campaign.
By all accounts, A-Rod and Diaz had broken it off shortly after the Yankees' season ended.
But the split apparently didn't take -- not unusual, according to one pal of the couple's.
"They break up and get back together all the time," the source told Us magazine.
Rodriguez -- also known as Stray-Rod for his wandering romantic eye -- has been doing his best recently to be true to Diaz.
"He has actually been trying to be on good behavior," a source close to A-Rod recently told E