Blalock's two-run double in the 11th inning rallied the streaking Rangers to a 6-5 victory over the Mariners on Wednesday night.
Wladimir Balentien's RBI double in the top of the 11th had given the Mariners a 5-4 lead.
In the bottom half, Michael Young led off with a single off Morrow (0-2). Josh Hamilton walked and one out later, Blalock's line drive one-hopped off the wall in right-center chasing home both runners as teammates streamed out of the dugout in celebration.
"It was great to get that hit off Morrow. The guy's got some of the best stuff in the league," Blalock said. "I was looking for a fastball I could jump on. We did a great job to grind it out for the win."
C.J. Wilson (2-2) pitched two innings for the Rangers, who won for the ninth time in their last 11 games.
Young's throwing error in the 11th provided an opening for the Mariners to score the go-ahead run, but Young got a chance to redeem himself in the bottom of the inning.
"I didn't give one thought to it," Young said. "I was getting ready to have a good at-bat. If I start thinking about something that happened earlier in the ballgame, good or bad, I'm not giving it my best effort."
Beltre and Johjima's homers staked Seattle to a 3-0 lead before Chris Davis' fourth-inning RBI single got the Rangers on the board, and Hamilton tied it at 3 with his two-run shot in the fifth.
Hamilton homered for the second time in as many nights after returning from a 13-game stint on the disabled list due to a pulled ribcage muscle.
Branyan's two-out solo shot in the sixth put Seattle back in front, but rookie Elvis Andrus' two-out RBI triple in the sixth tied the game at 4.
He also came up with a spectacular defensive play with a runner on first and two out in the eighth, ranging behind second base to glove Franklin Gutierrez's sharp ground ball and throwing out Gutierrez at first.
Mariners starter Jarrod Washburn allowed four runs and seven hits in six innings, striking out five and walking four.
Washburn kept the Mariners in the game against a lineup that leads the majors in homers on a night when the wind was blowing hard to right field.
"They're a very good hitting ballclub, especially with the wind howling out like that," Washburn said.
Texas starter Brandon McCarthy left after seven innings, allowing four runs and five hits. He struck out seven and walked one.
In an effort to energize his lineup, Seattle manager Don Wakamatsu made two changes, giving Ronny Cedeno his third start of the season at shortstop in place of slumping Yuniesky Betancourt, and giving Balentien his 10th start in left field for Endy Chavez.
Seattle had scored two runs or fewer in five of its previous seven games and a total of 16 runs in that seven-game span. The Mariners entered the game with a team batting average of .256, third from the bottom in the AL.
"It was nice to see the power production," Wakamatsu said. "The guys played hard all night. I'm proud of them."
Rangers closer Frank Francisco remained sidelined and won't be available until at least Friday due to biceps tendinitis. ... Wakamatsu had a pregame talk with Betancourt, who's in a 2-for-18 slide. "Historically his lack of patience at the plate is something we've talked about," Wakamatsu said. "As a coaching staff, we can't hit for him." Betancourt has two walks in 120 plate appearances. ... Seattle DH Mike Sweeney is still out with lower back spasms. ... Mariners LHP Ryan Rowland-Smith is scheduled for another bullpen session on Thursday, and then will be sent to extended spring training. Rowland-Smith has been on the 15-day DL since April 15 with left triceps tendinitis.