Kremer (6-2) allowed two runs on five hits and walked two while pitching a couple of hours from where he grew up in the Central Valley city of Stockton.
LaMonte Wade Jr. splashed a home run into McCovey Cove leading off the bottom of the first. Between innings, streamers flew to commemorate the 100th splash hit in Giants history. Logan Webb had to pick up a stray stream before throwing a pitch in the top of the second.
Félix Bautista, the Orioles' third reliever, struck out the first two batters of the ninth then surrendered Casey Schmitt's double before striking out pinch-hitter Michael Conforto to finish for his 15th save.
Webb (4-6), who went 3-0 in May, lost for the first time in six starts since a defeat to St. Louis on April 27. The right-hander gave up three runs on four hits, struck out six and walked one in seven strong innings.
In a play that mattered in a one-run game, Orioles right fielder Anthony Santander threw out Brett Wisely at the plate in the third on a single by J.D. Davis to save one run then Mike Yastrzemski followed with a tying double.
Baltimore took a 10-9 lead in the all-time series while playing its first game in San Francisco since 2016, when the Orioles won three of four here that August.
The schedule worked out beautifully for Baltimore manager Brandon Hydeh to spend two nights back home in Santa Rosa, and he reflected on there devastation back home from the Northern California wildfires that affected his city in 2017 and 2020.
He was thrilled parents Barry and Lucy would attend all three games of the series along with a rotating group of friends.
Hyde became a bit nostalgic driving into San Francisco upon arrival, too.
"I have special memories of games, watching Joe Montana with the Niners and watching Will Clark with the Giants back in my younger days with my dad and friends," he said. "I have some cool memories here, too, on the coaching staff with the Cubs. To be here in the Bay Area to have a lot of people here, people watching from home, I ran into a lot of people last night that I hadn't seen in a while, big Orioles fans now out here in the North Bay. Hopefully we can play well in front of them this series."
Orioles: CF Cedric Mullins isn't ready to begin rehabbing his strained right groin. ... RHP reliever Mychal Givens was placed on the 15-day injured list with inflammation in his pitching shoulder. Givens felt the discomfort after his last outing Wednesday against Cleveland and the hope is he will return in the minimum time.
Giants: Davis was hit on his left wrist by a pitch from Yennier Cano in the eighth but stayed in the game. ... OF Conforto was doing better recovering from a bruised left heel that forced him out of Tuesday's game against the Pirates and an MRI exam showed no structural damage. Manager Gabe Kapler was hopeful to get him in the game. ... 2B Thairo Estrada (sprained left wrist) hit off a tee and "that's going to tell us a lot," Kapler said.
Baltimore recalled LHP Bruce Zimmerman from Triple-A Norfolk.