The Rangers have won four of five games from the Astros heading into Sunday's season finale between the future American League West rivals. Texas has captured the Silver Boot from Houston in each of the last six years and has taken 18 of the last 23 games overall against the Astros.
Houston has lost 15 of its last 20 overall to fall to a season-high 11 games under .500.
Harrell (6-5) pitched 5 1/3 innings and allowed seven hits and five runs, with the Rangers erasing a 3-0 deficit in the span of two pitches -- a two-run single by Adrian Beltre and the long home run to left-center field off the bat of Cruz.
"He was getting a lot of quick outs," Rangers manager Ron Washington said. "I looked up there in the fifth inning and he had 48 pitches. The kid was getting a lot of quick outs. We were attacking him. Then, we finally opened up on him."
It was only a night earlier the Rangers had scored five runs in the fifth inning against Jordan Lyles following an error by third baseman Chris Johnson.
Harrell was indeed rolling through five innings, holding the Rangers to two hits and no walks.
Craig Gentry and Ian Kinsler jumped on Harrell in the sixth with singles on first pitches and were moved into scoring position on an Elvis Andrus sacrifice bunt. Michael Young followed with a chopper back to the mound, and Harrell immediately looked toward third, where Gentry was caught in no-man's land.
Gentry was able to scramble safely back to third when catcher Chris Snyder dropped the ball during the rundown, loading the bases with one out. Beltre stroked a 2-1 pitch into the outfield for a two-run single to cut the lead to 3-2 before Cruz sent the next pitch 431 feet over the fence to put the Rangers in control.
"The ball that was hit back to me, that was my fault," Harrell said. "I should have looked him back to third and then gone to first to get the out. I made the wrong decision, so it really cost us."
Snyder understood the magnitude of not finishing the play.
"I kicked it when the ball came to me and kind of cost ourselves an out there, and a team like this, you can't give them outs," he said.
After giving up the homer to Cruz, a visibly upset Harrell leaned over with his hands on his knees and stared at the ground as Cruz circled the bases. He was pulled by Mills after David Murphy followed the Cruz homer with a single.
"The only thing different in the sixth inning than the first five was that they started to ambush and balls were finding holes," Snyder said. "He still had the same stuff. We were pitching aggressive, we were pitching with what worked and when the situations arose, we're fighting to get a double play right there and get out of it. The best pitch to go with to get a double play is a sinker. He's got a good one. The ball just started finding the holes."
Texas starter Justin Grimm (1-0) delivered a quality start in his Major League debut by allowing six hits and three runs, striking out seven. The Astros got a solo homer from Jed Lowrie in the first inning -- his team-high 13th of the year -- and took a 3-0 lead in the fifth on an RBI double by Justin Maxwell and RBI single by Jordan Schafer.
"[Grimm] threw well," said Astros first baseman Brett Wallace, who was optioned to Triple-A Oklahoma City after the game. "He was aggressive and he was around the zone and he threw pretty well. I think for a kid making his debut, they usually have some nerves. But after Jed homered, he settled in and really made some pitches when he needed to, got out of some jams and kept guys off-balance."
The Astros' offensive woes were summed up in the eighth inning, when they had runners at second and third with no outs and couldn't score. Houston, which had five doubles, was 2-for-13 with runners in scoring position and struck out 10 times.