And after Mancini left the game, the Orioles went on to lose their eighth straight, 8-3 to the Athletics.
X-rays revealed nothing more than a bruised left elbow, although Orioles manager Brandon Hyde told reporters Mancini was "doubtful" to play Thursday night, when the Orioles open a four-game series in Seattle.
Mancini was hit by a 92 mph fastball from A's right-hander Chris Bassitt.
"I didn't think there was anything broken," Mancini told MLB.com. "But it's always good to know that for a fact and get the X-rays just to make sure."
Mancini is batting .304 with 16 home runs and 35 RBIs, ranking among the top 10 in the American League in batting average, slugging percentage, on-base plus slugging, runs, hits and total bases.
Hyde admitted he "expected the worst" when he came out of the dugout to check on Mancini, who slumped to the ground after being hit.
"It didn't look good when I went out there," Hyde said. "He was in serious pain. So you're hopeful, and we got lucky."
Outfielder Dwight Smith Jr. is expected to rejoin the Orioles in Seattle after being on the seven-day concussion list since June 7, a day after crashing into the outfield wall in Arlington, Texas.
The Orioles plan to send right-hander Dylan Bundy (3-8, 4.44 ERA) to the mound against the Mariners. Bundy has pitched better than his record this season, allowing more than three earned runs only three times in 14 starts. He's 1-0 with a 1.23 ERA in three career appearances against Seattle, including one start.
The Mariners plan to use an opener out of the bullpen before turning the ball over to veteran left-hander Wade LeBlanc (3-2, 6.20 ERA). In six career games against Baltimore, including four starts, LeBlanc is 1-2 with a 3.51 ERA.
LeBlanc pitched well in his first two games following an opener before allowing six runs in 2 2/3 innings of an 11-2 loss Saturday at Oakland.
"It just seemed like they were on everything I threw," LeBlanc told MLB.com, referring to his off-speed pitches. "If they're looking for what I was throwing, and I'm not making an adjustment, that's embarrassing."
The Mariners, who are in last place in the AL West, continue their week of hosting cellar dwellers after salvaging the finale of a three-game series against Kansas City, winning 8-2 Wednesday at T-Mobile Park. Domingo Santana hit two home runs with five RBIs and left-hander Marco Gonzales pitched 6 2/3 strong innings to win his third straight start.
The Mariners also got some good news on the injury front as an MRI revealed no additional damage to longtime ace Felix Hernandez's ailing right shoulder. Hernandez left early in his first rehab start for Triple-A Tacoma last week.
"It was just a shoulder fatigue-type situation," Mariners manager Scott Servais said.
--Field Level Media