Chapman threw 25 pitches on Friday -- each of them registering at least 100 mph -- and set a new personal best with one pitch that clocked in at 105 mph and three that reached 104 mph.
"I'll go on record and say that's the best velocity I've seen," Padres manager Bud Black said. "That's a legit No. 1 [fastball]."
Chapman's fastest pitch before Friday was 103 mph. The velocity of each pitch is determined using a league-wide MLB pitch FX computer that triangulates the calculation.
Chapman entered the game with two outs in the seventh inning, just after San Diego had taken a 4-3 lead, to face Adrian Gonzalez. And the Padres slugger struck out by swinging and missing at three consecutive pitches that reached 102 mph, 102 mph and 103 mph, respectively.
"As far as just the fastball itself, it's obviously hard, but you see it," Gonzalez said. "It's something that if I was to face him 15 times in a season ... it's like Hong-Chih Kuo from the Dodgers, where at the beginning, it's like, 'Man, this guy throws really hard,' and then over a certain amount of at-bats, you start seeing the ball better against him."
In the following inning, Chapman hit 104 mph twice and 105 mph once in an at-bat against Tony Gwynn that ended with Gwynn striking out looking on the seventh pitch that grazed the outside corner and registered 102 mph.
"I've seen 100 [mph] before and I've seen 101 before, but not on a consistent basis like that," Gwynn said. "He's got a live arm, to say the least.
"The best thing you can do is just try to slow everything down, because if you're going fast, you're not even going to put the bat on the ball. That's what I was trying to do is trying to be slow and get my foot down a little earlier than normal and try to work my hands."
Overall, Chapman walked one batter and did not allow a hit over 1 1/3 innings in his first action since Sept. 20 at Milwaukee. Of the 159 pitches he's thrown in the Majors, 74 of them have reached at least 100 mph.
"That's why we didn't pitch him for a couple of days," Reds manager Dusty Baker said. "A guy that throws that hard, he's going to be a little tender. We certainly have to preserve and take care of him. The more rest we can give him and more we spot him for certain periods of time, the better he's going to be."