But the Royals were ready. Gordon, Salvador Perez and Billy Butler each hit a home run in the first three innings as the Royals jumped out to a 4-0 lead.
"Same ballpark, same rain delay, same weather conditions," Orioles manager Buck Showalter said. "They did a better job with it than we did."
Mendoza certainly did a better job than Orioles starter Chris Tillman early in the game -- despite a couple of false starts to his pregame warmups. Mendoza worked six shutout innings before yielding three runs in the seventh.
"For six innings he was really good, very efficient with his pitches, getting quick outs," Royals manager Ned Yost said. "Not really in much trouble and when he did, he made pitches to get out of it. Did a nice job. Just kind of unraveled on him in the seventh inning."
Tillman, on the other hand, was greeted by Gordon's leadoff home run in the first inning on his third pitch.
"We knew he had a pretty good fastball and that's what I jumped on early," Gordon said. "Then he started mixing it up a little bit and he struck me out two times in a row."
Gordon drove the ball into the left-field seats, his fourth game-opening home run this season and ninth in his career. He also did it in the series-opening victory on Thursday night.
"I'm maybe a little more aggressive, going up there ready to hit and it's not always going to be that way, but right now it just feels like the thing to do," he said.
Perez clouted a two-run homer off Tillman in the second inning after Lorenzo Cain's single. It was Perez's second homer in two nights and his eighth in just 37 games since coming off the disabled list.
Then Butler got into the act in the third inning, pounding a 3-0 pitch from Tillman into the center-field seats. The solo shot gave him 24 home runs, adding to his career-high total, and gave the Royals a 4-0 lead.
"For me, it's huge and great plays by the defense, too," Mendoza said. He got excellent plays from infielders Chris Getz, Alcides Escobar and Eric Hosmer.
Tillman finally stopped the homer-an-inning trend with a scoreless fourth. A bit of déjà vu for Tillman. In his only other start against the Royals, July 29, 2009, he gave up three homers, but all were solo shots (by Alberto Callaspo, Mike Jacobs and Miguel Olivo) and the Orioles won, 7-3.
His time ran out in the sixth inning when, after two outs, he'd hit Perez with a pitch, prompting a flash of anger from the Royals' catcher, and walked Jeff Francoeur. Both runners scored after reliever Miguel Socolovich took over, Perez on Hosmer's single and Francoeur on a delayed double steal for a 6-0 lead.
Francoeur's steal of home was the Royals' first since Yuniesky Betancourt did it against Cleveland on Sept. 19, 2010.
Gordon's second homer led off the seventh inning against Socolovich, sending a 3-2 pitch over the left-field wall. It was the second multi-homer game of his career; he also hit two homers on Sept. 2, 2007, at Minnesota.
Even so, the Orioles made Yost nervous.
"Those guys have the propensity of battling back in those games," Yost said. "It was the seventh inning and we were up 7-0, but I didn't feel safe."
Yost felt less safe in the bottom half when things deteriorated quickly for Mendoza. His shutout came to an end with Wilson Betemit's walk, Chris Davis' single and Manny Machado's RBI double down the left-field line. Omar Quintanilla followed with a two-run single to center and Mendoza's outing was abruptly over with the score, 7-3, and none out.
However, reliever Kelvin Herrera came in to stop the bleeding with two scoreless innings and Tim Collins closed out the game with a perfect ninth.
"Good pitching all the way around," Yost said.
The Royals also are on a power spree with seven home runs in the first three games of this series.
"It's the park," Yost said. "Those balls don't go out in our park, but they go out in this park. ... You play the park."
The victory, the Royals' fifth in their last seven games, moved them into a tie with Minnesota for fourth place in the American League Central. They'd been in sole possession of the cellar since July 28.