He started the rematch that ensued the next day (1 August), throwing 148 pitches while holding Tohoku High to two runs in a 6–2 complete game win and leading the school to a third straight appearance in a national tournament. Sato took the mound against Chiben Gakuen Wakayama Senior High School in the first round of the 89th National High School Baseball Championship that followed on 9 August, holding the team to just two runs while striking out 17 in a 4–2 complete game win. While he gave up a home run to junior and noted cleanup hitter Masaki Sakaguchi (currently a third baseman for Tokai University) in the sixth inning, he threw a pitch that the radar gun at Koshien Stadium clocked at in Sakaguchi's next at-bat in the eighth, tying the highest speed ever recorded in the tournament (since the radar gun began being used in 1980) marked by current Yokohama BayStars right-hander Hayato Terahara as a senior for Nichinan Gakuen High School in 2001. He struck Sakaguchi out looking in that at-bat, throwing a total of 19 pitches clocked at or above in the same game. In the fourth inning of the second-round game against Chiben Gakuen Senior High School (the Nara champions) on 15 August, Sato threw a pitch clocked at , setting a new tournament record for pitch speed (as per official stadium radar gun readings). He gave up five runs in the very next inning, however, allowing eight hits and five walks in a 5–2 complete game loss. While he made three appearances in national tournaments during his three-year high school career, he never succeeded in getting past the second round. Sato was chosen to play in the U.S.−Japan High School Baseball Tournament (organized by the Japanese Educational Resource Center in conjunction with the Major League Baseball Urban Youth Academy) as a member of the Japanese team later that summer, clocking a new personal-high during the tournament. Sato was one of the most highly touted players going into the 2007 NPB high school draft, attracting the attention of scouts for not only his fastball but also his hard slider and being dubbed one of the "High School Big Three" along with Osaka Tōin Senior High School slugger Sho Nakata and Narita High School right-hander Yuki Karakawa. The Sendai-based Tohoku Rakuten Golden Eagles, Swallows, BayStars, Chunichi Dragons and Yomiuri Giants all selected Sato with their first-round picks, but the Swallows drew the winning straw, signing him to a base salary of 15 million yen, a signing bonus of 100 million yen and additional performance-based incentives and presenting him the uniform number 11 on 11 November.