Ackley swung at a hanging curveball and belted it to right field, and White Sox outfielder Alex Rios retreated a few steps and leaped slightly to haul it in.
It didn't seem like a very important moment in the game at the time, but after Humber had retired Brendan Ryan in the ninth inning to complete the 21st perfect game in Major League history, everyone was asking Ackley about it.
Because it was, by far, the closest the Mariners had come to getting a hit, or even a baserunner, in the landmark 4-0 loss.
Usually the recaps of perfect games and no-hitters show at least one or two diving stops in the infield or highlight-reel grabs in the outfield. Not this one. Rios' just-a-bit-more-difficult-than-routine snag was it.
"At that point, that early, nobody's really thinking about anything other than trying to get hits," Ackley said. "You're only down two or three runs at that point, just trying to get runners on, and you don't really think of it that early that this might be the only chance you've got."
Rios agreed, acknowledging that it wasn't exactly a basic play but that it wasn't one that gave him pause, either.
"He hit that ball pretty hard, and actually, as you probably saw, I had to jump a little to get that ball. But I never thought that it was going to be the closest to being a hit in that game," Rios said.
That was how it went for Humber, who didn't reach a three-ball count until encountering two of them in the ninth inning and got the perfecto done in 96 pitches. It was the most economical perfect game since David Cone of the Yankees needed only 88 to dispose of the Montreal Expos on July 18, 1999.
Aside from Ackley's screamer and a flare to left field in the seventh inning off the bat of Mariners third baseman Kyle Seager that was easily handled by Brent Lillibridge, Humber's outs came on strikeouts (nine), weak groundouts (five), shallow flyouts (five), pop flies to the infield (five) and a soft liner by Ichiro Suzuki in the first inning.
"The ball that was hit to Rios ... [Ackley] squared it up to right field and he made a nice catch on that," Humber said. "I don't know, for the most part, I was not thinking about any of that. I was just happy that they were making us plays and keeping us in the lead, more than a great [play] to save my no-hitter, perfect game."
Quick outs, soft outs, easy outs and 27 of them in a row: it all added up to a very tough piece of history for the Mariners to suffer through.
"It's hard to watch, especially when you know your team is being aggressive and trying to get pitches to hit," Mariners left fielder Chone Figgins said. "He was ahead and he stayed ahead, and he wasn't in the strike zone too much, and if he was, it was a pretty good pitch."
That was about all that could be said in a quiet, nearly empty Seattle clubhouse. The players who did talk showed a great eagerness to reverse the momentum as soon as possible, which would be Sunday afternoon.
And their manager, Eric Wedge, summed up the general theme of the day, which by and large was a collective cap-tip to a historic Humber.
"Guys were trying to do everything," Wedge said. "He was obviously pounding the zone, looking ahead, so we were trying to get on some pitches earlier in the count, but we just kept mishitting balls all day long. He did a good job spotting his fastball, he cut the ball a little bit, worked his breaking ball in when he needed to.
"He just kept us off-balance all day long."