The Draft Day star was spotted at the West Virginia Power's stadium with her parents, sister and three children: Violet, 8, Seraphina, 5, and Samuel, 2.
Garner, 42, cheered on the team to victory as spectators Tweeted their excitement at watching her return to her roots. (She even posed with the Power's mascot, Chuck!)
The game was part of the actress's low-key weekend trip to see family and friends – before she flew solo to meet husband Ben Affleck for their anniversary.
After grabbing dinner with friends Thursday night, Garner stopped by her alma mater, George Washington High School, on Friday. She took in the Power game Saturday evening.
But Affleck, who has been in Detroit shooting his role as the Caped Crusader in Batman vs. Superman, was nowhere to be seen.
Though his gambling has been making headlines, sources say he and Garner are still going strong.
"She never understood his gambling obsession and she doesn’t want him to be in the news [for it]," one insider told PEOPLE of Garner. "[But] she's the most patient wife ever and is still very much in love with Ben."
Despite Affleck’s absence from the weekend getaway, the couple celebrated nine years of marriage together Sunday. Affleck, 41, bought Garner jewelry from Barneys in Beverly Hills last week, and she joined him in Detroit after sending their kids and nannies back home to Los Angeles from Charleston. The two dined at Bistro 82 in Royal Oak, Michigan, according to the French restaurant's Facebook page and Tweets from onlookers.
Reporting by ANDREA BILLUPS and PERNILLA CEDENHEIM