Jake Thompson, the Phillies' top pitching prospect, will make his major-league debut on Saturday when he starts for the Phillies in San Diego.

The 22-year-old righthander registered a 1.21 ERA in his final 11 starts with triple-A Lehigh Valley. Thompson was acquired last summer from Texas as one of the key returns in the trade that sent Cole Hamels to the Rangers. He was dominant at the end of last season with double-A Reading and made a good impression on the Phillies during a stint in major-league spring training.

Thompson throws a low-90s fastball with a curveball, change-up and slider. The curveball has made great strides this season to pair with the already effective slider. He possesses great command of his fastball.

"I know he's got Major League stuff, and I'm anxious to see him perform," manager Pete Mackanin said. "We'll find out Saturday. It's his debut. I don't know what to expect."

Thompson fills the void left by Aaron Nola, who went on the disabled list on Wednesday with a right elbow strain. Thompson was scheduled to start Friday night for the IronPigs but will instead pitch a day later for the Phillies. The team's other starters will each be pushed back a day.

Thompson will be the 2,000th player to ever play for the Phillies. He is the third player acquired in the Hamels trade to reach the majors, joining Alec Asher and Jerad Eickhoff. Outfielder Nick Williams could join the Phillies sometime in the final two months, and catcher Jorge Alfaro could arrive next season.

Hernandez' mishap

Cesar Hernandez represented the potential winning run in the ninth inning Thursday, but he ended the inning when he was caught stealing second base. Hernandez easily beat the throw but came off the bag when he slid. The rally was over with Aaron Altherr at the plate.

"We were disappointed in that," Mackanin said. "He stole that base easily and slid past the bag, and we've addressed that at length with him because he has a tendency to do that. We've talked to him about it and worked on it. Unfortunately it came at a bad time, the winning run on base in the ninth inning. Disappointing. But we're going to continue to work with him."

Hernandez went 1 for 4 to bring his season average to a team-high .294. He turned his season around at the end of June and is batting .374 since June 27. But base running has been his flaw. Hernandez has been caught stealing seven times this season in 17 chances. He has also been picked off twice.

Extra bases

Giants reliever Sergio Romo was the first pitcher since 2009 to earn a win without facing a batter. The lone out he recorded was when Hernandez was caught stealing. . . . Jeremy Hellickson will face San Diego lefthander Christian Friedrich in Friday's series opener. The Phillies will also see two of their former minor-league pitchers when they face Paul Clemens and Jarred Cosart.