The ball landed amid a crowd of some 100 drifting kayaks and canoes, but the 22-year-old had gotten the jump. Oh, and he blocked off a kayaker and fought off a canoe with his arm.
"Anything goes out there," Mullin said. "I would have knocked over a nun. If I was going in the water, I was getting that ball."
At Monday's Century 21 Home Run Derby, the fans in the drink enjoyed the night's revelry. They started chants, played to the cameras, waved signs ("Hey David, Hit it to Wright") and let out sharp cheers whenever one of the Derby's three left-handed hitters came to the plate.
But the moment a ball dropped into the water, any and all decorum that once existed swiftly vanished.
"I'll dominate anybody out here," said Drew Haid, 22, of Pittsburgh as he coasted in a rented kayak. "If it comes within 20 feet, I'm getting the ball. There will be oars to the face, anything. All that matters is getting the ball."
"It can get pretty aggressive out here," said Ken Schultz, 37. "You hear the crowd and the announcer and everybody just dives in."
And there was plenty of it on Monday. Ortiz dropped five into the water in the first round alone. And both Ortiz and Philadelphia's Ryan Howard did what only one person had done (during a game) in the park's six-year history: reach the river on the fly, a minimum 454-foot drive.
For Mullin, at least, reaching the ball proved to be the simple part. When he tried to climb back aboard with his buddy, Jarrett Haynes, the canoe become engulfed with water and sunk straight down. Loyally clinging to his ball, he spent more than 10 minutes in the water before being rescued by a worker.
Worth it? "Oh, yeah, definitely. It was great," he said.
The sentiment was collectively shared in the stadium, most suggesting the Derby offered far more appeal than Tuesday's game.
"It's pure action, excitement," said Larry Gerken, 31, of Pittsburgh.
"Growing up, that's what I always watched. It's just a great event, watching guys like David Ortiz crank them out. That's what you want to see," 17-year-old Andy Burlett said before the home run contest began.
He had just caught a ball off the bat of Ichiro Suzuki during batting practice in right-field's Section 144, where he sat with his father. Contrasting the fierce scene on the water, the experience in the stands was decidedly calm. Relatively, at least.
"Stay in your area and don't run anybody over," said Burlett, explaining the unwritten rules governing fan behavior. Then he smiled. "That doesn't always happen, though."
And never on the water, where the television commentators on ESPN had plenty of fun with the scene. The fans, who rented the 40 canoes Kayak Pittsburgh was selling at a landing point in center field and also came with their own crafts, returned the favor.
Many had come looking for tickets to the event, but were not willing to let their fun end once they had been shut out.
"This is just such an exciting event," said Patrick Boylan, 17. "It might be more fun on the water."
David Briggs is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.