Normally when a major leaguer makes a rehab appearance in the minors, his presence swallows up all the fans attention.

On Tuesday at the Durham Bulls Athletic Park, Edinson Volquez had to share the spotlight. Volquez may have been making a possible final tuneup before joining the Reds' rotation, but he was followed up by Aroldis Chapman. And as hard as Volquez may throw, and as tough as his changeup can be to hit, the real buzz came when Chapman came in and started generating triple digits on the stadium radar gun (and the BA Stalker gun as well).

In some ways, it was fitting that Volquez and Chapman pitched on the same night. For Volquez, this was likely a last or second-to-last tune-up before he joins the Reds' big league rotation as he returns from Tommy John surgery. For Chapman, the recent move to the bullpen (this was his third outing as a reliever) likely means he'll moving up before long to help bolster a bullpen that has been the team's biggest weakness.

"This guy could change the pennant race," a scout said before quickly adding, "if he can throw strikes."

It was worth adding the caveat. The first pitch out of Chapman's hand was a 99 mph strike. He got to 1-2 on Dioner Navarro with an sharp 89 mph slider that would freeze just about any hitter, but then he humped up and overthrew a 103 mph fastball that hit Navarro. That ended up being a snapshot of what Chapman did on Tuesday–he showed lots of velocity and sometimes unhittable stuff, but he also was very prone to losing a pitch every now and then, with painful and sometimes scary results.

Navarro ended up moving to second on a ground out that Chapman hopped off the mound to field himself, and Navarro ended up scoring when Chris Valaika threw wildly on a grounder to second. But Chapman settled down to strike out hot-hitting top prospect Desmond Jennings with three straight fastballs, the first at 99, the second at 100 and the third at 101.

Chapman's second inning was rougher. Durham shortstop J.J. Furmaniak battled him for a 11-pitch at-bat by fouling off fastball after fastball after the count worked to 2-2. Chapman did eventually go back to his slider –Furmaniak fouled one off six pitches into the at-bat, and Chapman bounced one in the dirt 10 pitches into the at-bat—before Furmaniak took the 11th pitch and singled it to the opposite field.

That was the third and last slider that Chapman threw on Tuesday. For the next four batters it was all heat, all the time. He once again picked up a three-pitch strikeout when Justin Ruggiano went down on a 101 mph fastball. But from there on, Chapman's control really began to waver. He plunked Dan Johnson with a 99 mph fastball and then fell behind 3-0 to Joe Dillon before getting Dillon to fly out to center field.

Chris Richard, the final batter he faced, also saw plenty of fastballs. After Richard fouled off a 100 mph heater on the first pitch, Chapman again lost a pitch–this one was a 100 mph fastball that was headed just below Richard's chin. Richard alertly fell backwards out of the way in time, while the pitch got away from catcher Ryan Hanigan and went to the backstop for a run-scoring wild pitch. The Bulls' crowd audibly gasped as Richard's dove out of the way–when a lefty throwing 100 mph loses a pitch near a lefthanded hitter's head, there's reason to worry about more than just whether a run will score on the play. To Richard's credit, he dusted himself off, got back in the box and eventually chopped an opposite-field single that scored a run.

Overall, Chapman took the loss and gave up four runs (three earned) while getting five outs, three via strikeout. He didn't have a lot of problems throwing strikes. Of his 40 pitches, 27 were strikes. He did have some problems with finishing off batters; both of the hits against him came on two-strike counts after hitters had fouled off previous two-strike fastballs. Chapman showed a slider that is a definite weapon, but he didn't seem completely comfortable using it late in the count.

Unlike his time as a starter, Chapman's velocity didn't vary much as a reliever. Of his 37 fastballs, 29 were thrown at 98 mph or better including one at 103, two at 101 and six at 100 mph. But when Chapman did miss, he missed badly. It's worth noting that Chapman showed the same hit-or-miss control in his bullpen warm-up. He showed several nasty sliders, but he also bounced a pitch that got away from the bullpen catcher and ended up rolling past the Bats' dugout.

"There are a lot of moving parts," the scout said in explaining why Chapman's control seems to come and go. The scout added that he liked how the 6-foot-4, 185-pound Chapman's delivery from the stretch does a good job of hiding the ball–something that's not easy to do with the lanky body and long arms that help explain Chapman's unrivaled velocity.