Harrison goes for a 10th consecutive winning decision over the Mariners on Sunday as the Rangers try to maintain their slim lead in the AL West.
Harrison (16-9, 3.36 ERA) is 9-0 with a 1.62 ERA in 14 games - 10 starts - against Seattle (70-76) since the start of 2009. He's won seven starts in a row versus the Mariners - three this year - including a five-hitter in a 4-0 road win July 15.
The left-hander's lone loss to Seattle came as a rookie July 31, 2008.
Another victory Sunday would make Harrison the Rangers' first 17-game winner since Scott Feldman in 2009, and would also ensure the club won't lose any more of its lead over Oakland this weekend for the West lead.
The Rangers' lead dwindled to two games Saturday, when they rallied to erase a six-run deficit but ultimately lost 8-6.
"This team never quits," said Feldman, who gave up six runs in 2 2-3 innings. "We kind of take it for granted sometimes what a competitive team we have and what a good team we have."
Harrison has been erratic lately, going 3-2 in his last five starts with a 1.66 ERA in the victories compared to a 9.00 ERA in the defeats. He was solid Tuesday, yielding two runs and five hits with six strikeouts in 5 2-3 innings of a 6-4 victory over Cleveland.
Texas outfielder Nelson Cruz is 5 for 12 with two doubles and three RBIs in his last three games after getting three hits and driving in two runs Saturday.
The last-place Mariners are getting plenty of opportunities to play spoiler, as their remaining 16 games are all against playoff contenders - Texas, Baltimore, Los Angeles and Oakland.
First baseman Justin Smoak had one of his best offensive displays of the season in Saturday's win, getting three hits including a homer and driving in three runs, snapping out of a 6-for-41 funk over the switch hitter's previous 14 games.
"I've been working really hard left-handed," Smoak said. "I've been trying to keep both hands on the bat and shorten it up a little bit. My swing got long. To come around on a fastball like that, that's a good sign."
Smoak, who arrived in the majors as a Ranger in 2010, is batting .318 with six homers and 18 RBIs in 17 career games in Texas as a visitor.
Mariners starter Blake Beavan (9-9, 5.01), a native of Irving, Texas, will get the ball in neighboring Arlington for the third time this season.
The right-hander split his previous two visits with widely differing performances. In the most recent outing May 30, he allowed five runs and eight hits in six innings of a 21-8 win.
Beavan could have used any production from the Seattle lineup April 10, when he yielded one run in 6 1-3 innings of a 1-0 defeat.
"It's hard to realize the good things from this park sometimes, because you're playing such an overpowering team in a great hitting ballpark here at the same time," Beavan told the Mariners' official website.
Beavan last got the ball in a 4-3 loss to Boston on Sept. 4, when he gave up four runs and eight hits - two homers - in 5 2-3 innings.