Santana, ranked by MLB.com as the Astros' No. 7 prospect, was hitting .304 with 13 homers and 52 RBIs in 84 games for the RedHawks when he was called up Tuesday to replace Dexter Fowler, who was placed on the disabled list.
"It was good to get him here and experience Major League pitching," manager Bo Porter said Sunday. "The struggles which he went through will help him as he moves forward. I talked to him after the game and told him, 'Hitting in the Minor Leagues, as you found out real quickly, it's different there.'
"Pitchers have the ability to throw ball-four pitches in different counts [in the Major Leagues], and that's why it's so important from a mechanical standpoint to be in a good position to hit from your posture and setup. That will help him moving forward."
Martinez, 26, was 5-6 with a 4.92 ERA in 16 games (12 starts) for Oklahoma City this year, allowing 76 hits and striking out 56 batters in 75 innings. Martinez pitched four games for the Astros last year, going 1-0 with a 7.15 ERA in 11 1/3 innings.
He was named the 2013 Texas League Pitcher of the Year after going 14-2 with a 2.02 ERA at Double-A Corpus Christi, setting a club record for wins before being promoted to Oklahoma City, where he pitched three games. Martinez made his Major League debut Aug. 21, 2013, at Texas.
"Just looking at the last few games and the condition of our bullpen, we felt it was important that he could get here and could give us extended innings, because those guys out there are tapped," Porter said. "It was Martinez's turn to pitch [at Oklahoma City], and we needed a long guy."
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.