Harper went deep for the first time in the AFL, pacing Scottsdale to a 13-9 victory over Peoria on Saturday.
Harper, the Nationals' first-overall pick in June, entered the game 3-for-12 for the Scorpions. Leading off the second inning against Padres prospect Erik Davis, Harper pulled the first pitch he saw over the right-field wall for a solo homer. The 18-year-old outfielder capped the scoring with an RBI double off the right-field wall in the eighth. He's now batting .353 with four RBIs for first-place Scottsdale.
Harper, who finished a triple shy of the cycle, signed with Washington out of the College of Southern Nevada, inking a $9.9 million bonus, a record for a position player. The Nevada native was named the winner of the Golden Spikes Award as the top amateur player in the county after batting .443 with 31 homers.
The Scorpions (11-6) fell behind early, trailing 7-3 after four innings. Brandon Belt (Giants), one of two Minor Leaguers with 20 doubles, 20 homers and 20 steals, sparked Scottsdale's rally, going 3-for-5 with three runs scored. Fellow Giants farmhand and AFL batting leader Charlie Culberson raised his average to .472 with a two-hit game, scoring four times and driving in three runs. Jordan Pacheco (Rockies) was 3-for-5 with two RBIs.
Diamondbacks prospect Josh Collmenter (2-0) took a no-decision after allowing six runs on eight hits over 3 2/3 innings. Fellow Arizona farmhand Daniel Stange (2-0) was credited with the win, surrendering a run on two hits in an inning of relief.
Jose Ruiz (Rays) paced the Saguaros' (4-12) offense with four hits and three RBIs. Dave Sappelt (Reds) was 2-for-6 with two runs scored and Joe Benson (Twins) smacked a pair of doubles in a losing effort.
Brad Brach (1-1) was tagged with the loss for the Saguaros, allowing two runs in an inning out of the bullpen.
Robert Emrich is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.