"My two-seam fastball was moving pretty well," he said. "They had more lefties in their lineup than I'm used to seeing, so that was an important pitch for me."
Keuchel, a 23-year-old University of Arkansas product, came on in relief of Rafters starter Charles Brewer in the second inning. The first batter he faced, Nationals prospect Bryce Harper, singled, stole second and scored on a two-out double by Scorpions first baseman Cody Overbeck (Phillies).
"I was originally scheduled to pitch last Saturday, but had to go out of town for my sister's wedding," explained Keuchel. "I knew I was going to pitch sometime today, so I started my bullpen [session] later and just tried to treat it like a start."
All of Keuchel's previous 33 outings this season -- 20 for Double-A Corpus Christi, where he went 9-7 with a 3.17 ERA, seven for Triple-A Oklahoma City and six for the Rafters -- were starts.
Keuchel settled in after Overbeck's double, retiring the next seven Scorpions in a row before Alex Hassan (Red Sox) led off the fifth with a base hit to left. Scottsdale loaded the bases with two more singles in the frame, but left three men on base when Keuchel struck out second baseman Joe Panik (Giants) to end the threat. The Scorpions were 2-for-11 with runners in scoring position.
The left-hander gave way to fellow Astros prospect Jason Stoffel in the sixth, having allowed one run on five hits in four innings. Keuchel improved to 3-2 in seven games for the Rafters.
Stoffel, Cole St. Clair (Dodgers), Bryan Woodall (D-backs) and Casey Crosby (Tigers) finished out the game for Salt River, combining to allow two hits over four scoreless innings. Crosby earned his first AFL save with a perfect ninth.
Third baseman Nolan Arenado (Rockies) and designated hitter Ryan Wheeler (D-backs) singled three times apiece for the Rafters. Tigers prospects Rob Brantly and Hernan Perez each had two singles and first baseman Ben Paulsen (Rockies) delivered a two-run double in the fifth inning. Salt River outhit the visiting Scorpions, 14-7.
Rafters leadoff man Adam Eaton legged out an infield hit with two outs in the eighth to extend his hitting streak to 17 games, the longest in the AFL this season. The Arizona prospect has reached base in each of his 28 Fall League games.
Scottsdale's Brandon Crawford (Giants) and Harper had compiled recent 16-game streaks, but both ended in the Scorpions' 6-4 loss at Surprise on Saturday.
Harper, who singled twice and scored the lone Scottsdale run, was the only Scorpion with more than one hit Tuesday. Shortstop Jean Segura (Angels) was the only Scorpions batter to avoid striking out.
Scottsdale starter Tyler Cloyd (Phillies) fell to 1-4 after allowing two unearned runs on six hits over four innings. The Scorpions committed all three of their errors in the game with Cloyd on the mound.
Salt River improved to 22-14 with two games remaining before Saturday's AFL Championship Game against the Surprise Saguaros.
Having thrown 66 pitches -- 41 for strikes -- against Scottsdale on Tuesday, Keuchel was unsure if he would be used in the finale.
"I've volunteered to pitch Saturday, even if it's only a situational thing," the left-hander said. "We definitely want to win this thing. Everyone on the team is pumped up for it."
John Parker is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.