Lopez closed out the year with an outstanding run in September (1.09 ERA), bringing his ERA for the season under 4.00 after it got as high as 4.72 in mid-August. Was it mostly luck, or did Lopez actually figure something out down the stretch? He said last summer that he was focusing on the mental aspect of the game instead of just trying to blow by hitters, continuing lessons instilled by Max Scherzer about scouting hitters, locating and changing visual angles. An important aspect of Lopez's development has been the slider that White Sox pitching coach Don Cooper taught Lopez in 2017. It has since become Lopez's best pitch by Pitch Values. Lopez's strikeout rate soared to 27.6% over the final month, and while it may have been mostly fluky, part of it may have been his maturation as a pitcher and the more granular scouting of his opponents. Further refinement of the changeup is still needed, but there is plausible upside here.

Acquired from the Nationals last offseason in the Adam Eaton deal, Lopez is one of many power arms the club has stockpiled. After 22 starts for Triple-A Charlotte, registering a 3.79 ERA and 1.24 WHIP with 131 whiffs in 121 innings, Lopez got the call to the majors, making his Pale Hose debut on Aug. 11. Lopez started eight contests, working at least six stanzas in all but one, an impressive feat in today's five-and-fly climate. A 65 percent left-on-base rate didn't do his ERA any favors, though a weak 15 percent strikeout rate didn't help either. Lopez displayed an above-average strikeout clip everywhere else, including a short stint with the Nationals in 2015, so expect the righty and his 95-mph fastball to pick up the pace as he further acclimates to major-league hitters. Lopez has the stuff to be a difference-maker down the line. For now, there will still be growing pains, working half the time in one the American League's friendlier hitting venues.

After dominating Double-A to begin the season, Lopez spent the second half bouncing between Triple-A and the majors, posting solid ratios at Syracuse despite a decline in his strikeout rate but mostly struggling for Washington. He flashed his upside in August, though, posting a 1.29 ERA and 13:4 K:BB in 14 innings over back-to-back starts against the Braves. The 22-year-old right-hander's big weapon is a fastball that averaged 95.8 mph in the majors, but he also mixes in a plus curveball and work-in-progress changeup. There are concerns about his ability to hold up as a starter given his slight frame, but his arsenal should allow him to thrive in a late-inning role if he is eventually moved to the bullpen. Traded to the White Sox in the Adam Eaton deal, Chicago will give Lopez every chance to stick as a starter, and a strong spring could put him in the rotation to begin 2017.

A year after a breakout performance that landed him near the top of the Nationals' prospect list, Lopez is still more future projection that he is finished product. His 4.09 ERA and 8.5 K/9 in 99 innings at High-A Potomac weren't exactly dominant, but his 2.5 BB/9 and 0.5 HR/9 indicate an ability to keep the ball in the lower half of the strike zone that will serve him well as he advances through the system. The 22-year-old right-hander fires a heavy high-90s fastball from an easy, repeatable delivery, and his curveball and changeup both have the makings of above-average pitches. Six-foot pitchers with big velocity tend to get typecast as relievers, and that could well be Lopez's eventual fate, but his athleticism and secondary offerings are strong enough to give the Nats every reason to keep him in the rotation as he works his way up the ladder.

Signed out of the Dominican Republic in 2012 as an 18-year-old, Lopez raced up prospect lists after a breakout season in which he struck out 70 batters in 83.1 innings between the New York-Penn and South Atlantic leagues. The right-hander features a heavy mid-90s fastball that he can crank up to near triple digits when he feels the need, plus a work-in-progress breaking ball and changeup, and if everything comes together, he'll give the Nationals yet another future ace to slot in alongside Stephen Strasburg and Lucas Giolito. Lopez is a long way from being in their company, though, and even the Yordano Ventura comps getting bandied around are very premature. The kid has massive upside, and that fastball is as close to a guarantee of a big league job as you'll find, but you may want to wait and see if he can dominate over a full season before anointing him as the next big thing.