Pedro Alvarez then belted a shot off Ventura headed for the bullpens in left-center field.
But Royals center fielder Lorenzo Cain raced to the warning track and timed his leap perfectly, grabbing the blast from beyond the fence and pulling it back in for the out.
Cain stumbled, regained his footing and fired the ball back into the infield as the crowd at Oriole Park at Camden Yards watched in disbelief.
Many in the crowd rose to their feet and gave Cain a solid ovation.
According to Statcast™, Cain covered 71.3 feet in 0.47 seconds, travelling at 18.3 mph. His route efficiency was 98 percent. On balls hit this season with an exit velocity of 106 mph and a 19-degree loft, the batting average has been .885 (54-for-61), according to Statcast™.
"It ranks pretty high," Cain said. "I just tried to get back and make a play. They did a great job of swinging the bats tonight, so I just tried to do everything possible to make plays tonight."
Cain nearly robbed the O's of another homer later.
"It hit off my glove," Cain said. "I should have caught it."
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.