With the Royals trailing by a run in the seventh inning, first baseman Eric Hosmer's leadoff slow roller off O'Day teetered along the third base line in front of the bag, between O'Day and third baseman Wilson Betemit, who were looming over it waiting for the ball to turn foul.
To the Orioles, it was no laughing matter. Hosmer later scored the tying run, and the Royals manufactured another in the eighth to beat the Orioles, 4-3, in front of an announced 26,714 at Camden Yards.
"I can honestly say I've never had that play before in my 20 years of playing baseball, and now I know for the next 20," O'Day said. "I was shocked to see the ball stay fair. First of all, he's a good runner. It's a smart play, for sure. It's a lesson learned. Next time, I'll get around to the other side of the ball and keep an eye on the runner, and hopefully keep him to first base."
The Orioles (29-18) wasted their 24th quality start this season -- an impressive six-inning, two-run effort from rookie left-hander Wei-Yin Chen -- losing just their second game in which their starting pitcher has gone six or more innings and allowed three or fewer runs.
The Orioles remained in first place in the American League East when the Boston Red Sox beat the Tampa Bay Rays on a walk-off homer by Jarrod Saltalamacchia.
Hosmer, part of a bottom third of the order that was 6-for-12, also drove in two runs, including the game-winning run off Pedro Strop (3-2) in the eighth, a one-out lazy single to left that ended Strop's streak of 142/3 scoreless innings.
"We knew we were going to have to score some more runs," Orioles manager Buck Showalter said. "Just a fine line there. They were due for some things to go their way. We battled. We had some opportunities. The bullpen pitched well, if you look at what they actually gave up."
After taking a 3-0 lead in the third inning -- highlighted by solo homers by Chris Davis and J.J. Hardy -- the Orioles couldn't muster any offense. They stranded nine base runners and had the leadoff batter on base in four of the final six innings, but only one runner reached second base in that span.
"As good as our bullpen has been, you can't expect them to pull that weight all season," said Davis, who hit his second homer in as many days with an opposite-field shot to left in the second inning. "There's got to be times when we go out there, like [Friday] night, and give our pitchers a six-run cushion, you know, something to work with. You can't expect those guys to come out there every day and pitch in a one-run game."
Chen, who left the game with a 3-2 lead, gave the Orioles the chance to win, giving the club his fifth quality start, including four at Camden Yards. Take away his last start, a forgettable 41/3-inning, six-run outing in Washington, and Chen has allowed three or fewer runs in each of his other eight starts.
The Orioles, who were stymied by Royals starter Felipe Paulino on May 16 to the tune of seven shutout innings, got to the 28-year-old right-hander with a pair of early solo home runs.
Davis took a 1-0 curveball from Paulino the opposite way to left-center field to give the Orioles a 1-0 lead.
In the third, Hardy hit his 10th homer of the season, putting a 94 mph fastball into the left-field stands.
Two batters later, Adam Jones tripled into right-center field, then came in to score on Matt Wieters' sacrifice fly to deep center.
In a tie game in the eighth, Strop, who had made 13 straight scoreless appearances, yielded a leadoff single to cleanup hitter Mike Moustakas, then issued a one-out walk to Alex Gordon and a single to Johnny Giavotella to load the bases.
Hosmer then singled to left just in front of Xavier Avery -- his second RBI of the day -- to give Kansas City a 4-3 lead. With the bases still loaded, Strop recovered, striking out Humberto Quintero and getting Mitch Maier to ground out to second.
Orioles designated hitter Nick Johnson just missed a two-run homer in the eighth that would have regained the lead late, but it was wide of the right-field foul pole by about five feet.
After Hosmer's double off O'Day, Quintero doubled down the right-field line to drive in Hosmer and tie the game at 3.
Maier -- in for starting center fielder Jarrod Dyson, who came out of the game with a right hamstring contusion after a collision with left fielder Gordon -- hit a single that dropped behind third base in front of Avery.
O'Day prevented further damage, striking out Alcides Escobar and Billy Butler to end the inning.
"Regardless of that happening," O'Day said, referring to Hosmer's double, "I need to make better pitches the next time. I went on to make some better pitches. I needed to start one batter sooner.
"It's the law of averages. Things like that are going to happen, and good pitchers will come back and get the next guy."
Before then, Butler had made it a 3-2 game in the sixth, leading off the inning with his 10th homer of the season, a towering blast off Chen that landed in the upper bullpen in left-center. Hosmer drove in the Royals' first run with a fifth-inning RBI single off Chen that followed Giavotella's leadoff double, which was the first time Chen allowed a Royals batter to reach scoring position.
"Compared with the last outing, I feel like I improved today," Chen said through interpreter Tim Lin. "But I still have a lot of room to improve. I feel my timing is better this time."