Peacock allowed one hit and struck out six over 5 2/3 shutout innings, pitching the Double-A Harrisburg Senators to a 3-2 victory over the Richmond Flying Squirrels.
Named an Eastern League All-Star earlier in the day, Peacock (9-2) took over for Erik Davis following a 45-minute rain delay in the middle of the first inning. He proceeded to pitch four hitless frames before Wes Hodges led off the fifth with a single.
The 23-year-old right-hander walked Charlie Culberson with two outs in the sixth and was lifted after 85 pitches.
The Nationals' No. 9 prospect, according to MLB.com, Peacock is having a breakout year. He leads all Minor Leaguers with 120 strikeouts and tops the Eastern League with nine wins while ranking second with a 2.14 ERA. The victories already are a career high for the 2006 41st-round Draft pick, who went 8-11 across two levels in 2009.
Three days before the Eastern League All-Star Game, he'll showcase his talents in the All-Star Futures Game on July 10 in Phoenix.
Wednesday was Peacock's second dominant performance in as many starts against Richmond. On May 13, he recorded a career-high 14 strikeouts and limited the Flying Squirrels to one run on five hits over seven innings.
Chris McConnell doubled home a pair of runs and Tim Pahuta homered and scored twice for the Senators in this one.
Reliever Daryl Maday (2-6) took the loss after allowing three runs on six hits with seven strikeouts over 5 2/3 innings.