Kyle Crick, Clayton Blackburn and Chris Stratton, the San Francisco Giants top three prospects according to FanGraphs, have yet to pitch above A-ball. Thus, they don't have the professional experience needed to make the opening day roster.
Joe Panik---their second-best positional prospect---has also yet to play in the upper levels of the minor leagues. His performance at Double-A this coming season will determine how quickly he gets to the big leagues, but he's not going to make the opening day roster unless a plague strikes the Giants middle infield.
Gary Brown---the number one prospect amongst position players---has received more minor league plate appearances than Brandon Belt, Buster Posey or Brandon Crawford, but there's no spot for him on the opening day roster.
Hunter Pence, Angel Pagan, Gregor Blanco and Andres Torres are firmly entrenched in four of the outfield spots, leaving only one opening for a bench player. Unless the Giants decide that Brown's ceiling is that of a reserve, he's going to start the season playing every day at Double-A or Triple-A—if he receives a promotion.
Amongst the Giants' other top-15 prospects, reliever Heath Hembree, starter Michael Kickham and outfielders Roger Kieschnick and Francisco Peguero have the best odds of making the opening day roster.
If one of the Giants five entrenched starters were to open the season on the disabled list as Ryan Vogelsong did last season, Kickham and Giants' minor league pitcher of the year Chris Heston would likely compete for the final rotation spot.
The Giants minor league system is short on upper level pitching prospects outside of Kickham—who had a 3.05 ERA in Double-A last season—and Heston, who put up a 2.24 ERA at the same level.
The Giants have six relievers under contract in Sergio Romo, Santiago Casilla, George Kontos, Jeremy Affeldt, Javier Lopez and Jose Mijares. That leaves one open spot for Hembree to claim, though a trade or an injury could open up an additional spot.
Hembree will likely compete with waiver claim Sandy Rosario and minor league free agents Scott Proctor, Jon Meloan and Chad Gaudin for a spot in the bullpen.
The Giants have one spot open for a reserve outfielder, and Peguero and Kieschnick appear to be the top candidates for that role. After two disappointing seasons at Double-A, Kieschnick broke out in Triple-A last season where he hit .306/.376/.604 before crashing into a wall and suffering a shoulder injury. The injury and his struggles in winter ball could push back his timetable for another season.
Peguero has the inside track on a roster spot after flashing a strong throwing arm and good athleticism in his brief cup of coffee with the Giants last season. Like Kieschnick, he struggled in winter ball this offseason, so he'll have to have a solid spring training to make the team.
Outfielder Juan Perez also has an outside shot to make the squad after he hit .302 at Double-A Richmond last season, earning a spot on the 40-man roster. Minor league free agents Cole Gillespie and Javier Herrera could compete with Perez, Peguero and Kieschnick during spring training for the final spot on the Giants' bench.
The prospects with the most potential—Crick, Blackburn, Stratton, Brown and Panik—need more seasoning in the minor leagues. All five could get a look during spring training, but none of them has much of a chance to make the team.
Instead, prospects with less upside but more upper level minor league experience like Hembree, Kickham, Heston, Kieschnick, Peguero and Perez, should have the best odds of making the roster out of spring training.
The Giants aren't likely to start the season with any of their elite prospects on the major league roster. However, of the current homegrown core of stars on the big league roster, only Brandon Belt made his debut by winning a job in spring training, and he was quickly demoted back to the minor leagues after struggling out of the gate.
Thus, it will be more interesting to see which Giants prospects make their debut later in 2013.
If Brown, Panik or one of the young pitching prospects flourishes in the minor leagues this season, it isn't hard to imagine them making an impact later in the season as Crawford, Posey, Matt Cain, Tim Lincecum, Madison Bumgarner, Sergio Romo and Pablo Sandoval did in recent seasons.