Fortunately for the 21-year-old right-hander, the Mariners had soon collected double that number of home runs and Walker settled down to help Seattle to a 10-4 victory.
Robinson Cano's three-run shot in the seventh inning highlighted a night with a season-high four home runs for the Mariners.
Mike Zunino had a two-run drive in the second, Michael Saunders added a pair on his long ball in the fourth and Brad Miller hit a home run two batters later to help the Mariners to their eighth victory in 10 games.
"I thought he threw pretty darn good," manager Lloyd McClendon said. "Command was a little shaky to start with, but I thought he settled down and threw some decent breaking balls, some decent changeups. Starting to find a rhythm a little bit. Did OK."
Walker said he tried not to get down on himself, but he knew that he could do a better job than he was doing early.
"I'm not swearing at myself, but I'm talking to myself: 'C'mon Taijuan. Just keep the ball down and get ahead in the count,' " he said. "[Monday] my fastball command wasn't there, so I relied on my changeup. That got me through it."
Rookie James Jones had a career-high four hits and his second three-steal game. He's the second player in franchise history and first since Ichiro Suzuki in 2004 to have at least four hits and three steals in a game.
Houston starter Collin McHugh (4-7) allowed five hits, five runs and tied a career high with three home runs in six innings.
"From the beginning of the game, he just really had trouble locating his fastball," manager Bo Porter said. "When you fall behind and get into predictable fastball counts, he ran into some guys that put good swings on it."
Walker has started four major league games and three have come against the Astros. He picked up his second win on Monday night and the first since he also beat the Astros in his major league debut on Aug. 30.
Houston's Jose Altuve went 0 for 3, but extended his franchise record by stealing a base in his seventh straight game. He leads the American League with 37 this season and his seven-game steal streak is the most in the majors since Chone Figgins did it in 2010.
He was plunked on the left elbow in the fifth inning, but appeared to be OK.
Alex Presley singled with one out in the first before Springer's towering shot, which bounced off the glass above the left field wall, gave Houston a 2-0 lead. It was the first career homer allowed by Walker and traveled an estimated at 445 feet, which is the longest ever hit to left field by an Astro.
Walker wasn't sure if that was the longest home run he'd allowed.
"I've given up a few that were pretty far," he said. "I didn't watch it. It was high enough. I didn't want to turn around."
Springer leads the Astros with 16 homers this season, which is a franchise record for a rookie before the All-Star break.
Logan Morrison drew a walk to start the second before Zunino's home run to the Crawford Boxes in left field tied it at 2.
Gonzalez put Houston back on top in the bottom of the inning with his two-out homer, which crashed off the foul pole in right field.
Zunino struck out with one out in the fourth inning, but reached first on a wild pitch. Saunders gave Seattle a 4-3 lead with his home run to the second deck in right field.
McHugh struck out Dustin Ackley before Miller's fifth home run this month pushed the lead to 5-3.
Houston optioned SS Jonathan Villar to Triple-A Oklahoma City and designated RHP Jerome Williams for assignment after the game. Williams had a 6.04 ERA in 26 games this season. ... Walker is the third pitcher since 2004 to face the same team three times within four starts, joining Wade LeBlanc and Justin Germano. ... The series continues Tuesday when Houston's Jarred Cosart opposes Hisashi Iwakuma.