Bret Saberhagen was drafted in the 19th round in 1982, out of high school in Northridge, California. A shortstop/pitcher in high school, he was well-regarded as an athlete, but worries about a sore arm kept him out of the early rounds of the draft.

He made his pro debut in 1983, going 10-5, 2.30 in 16 starts for Fort Myers in the Florida State League, with an 82/19 K/BB in 110 innings. Promoted to Double-A in July, he went 6-2, 2.91 in 11 starts. This was stunning performance for a 19 year old making his pro debut. He impressed everyone with his command of above-average stuff (92-93 fastball, good breaking stuff) and his composure that was well ahead of his years. I'd say you'd have to give him a Grade A- rating at a minimum, and maybe even a straight Grade A.
To go from a 19th round pick who signed late and had injury worries to Top Ten Pitching Prospect in one season was a precursor of things to come.

Sabes made the major league roster out of spring training in 1984. Used as a swingman, he went 10-11, 3.48 in 158 innings (20 relief outings, 18 starts), at age 20. His strikeout rate was rather low, with a 73/36 K/BB, but given his age this was hardly a major flaw. The following year he went 20-6, 2.87 and won the Cy Young Award at age 21, the youngest player so honored.

Saberhagen had problems staying healthy after his mid-20s, and at times he was erratic. But overall he was a very impressive pitcher, dominant at his best with exquisite command of above-average stuff. He finished 167-117 with a 3.34 ERA and ERA+ of 126. Lack of durability keeps him from Hall of Fame consideration, but his peak seasons were impressive indeed. Not bad at all for a 19th round pick. It's interesting to note that while the scouts were right in one way (injuries were a problem), every team had to be kicking themselves for letting him slip so long in the draft.

Complete list of pitchers drafted in the first round in 1982:
Jimmy Jones, RHP, Padres (high school, Texas)
Bryan Oelkers, LHP, Twins (Wichita State)
Dwight Gooden, RHP, Mets (high school, Florida)
Bob Kipper, LHP, Angels (high school, Illinois)
Duane Ward, RHP, Braves  (high school, New Mexico)
Mark Snyder, RHP, Indians (high school, Tennessee)
Rob Parkins, RHP, Red Sox  (high school, California)
Rich Monteleone, RHP, Tigers (high school, Florida)
Todd Worrell, RHP, Cardinals (Biola College)
Scott Jones, LHP, Reds  (high school, Illinois)
Billy Hawley, RHP, Reds  (high school, South Carolina)
Joe Kucharski, RHP, Orioles (University of South Carolina)

The only one of those guys who was in Saberhagen's class was Gooden, who won 194 games but who had his own set of issues.