SEATTLE -- Within the walls of the Mariners’ clubhouse, many have already met “Walter,” the imposing alter ego of Logan Gilbert. But on Tuesday night, the fiery and seemingly out-of-character second personality of the starting pitcher went mainstream.

On Gilbert's 101st and final pitch in a 3-0 win over the White Sox at T-Mobile Park, the towering right-hander blew a 98.6 mph fastball by AJ Pollock to strand two runners and cap his sixth scoreless inning. It was a tense sequence, with the tying run on third base and the go-ahead run on first.

Yet, Gilbert used every bit of his 7.5-foot extension down the mound, completely emptied the tank with his second-fastest pitch of the game, watched Pollock whiff and then clenched his fists and screamed with such raw emotion that brought to life the alter ego that’s been heard of, but never quite seen.

Gilbert might have taken the mound ahead of that moment, but “Walter” walked off.

“He is about as kindhearted, as nice -- I say a kid, but a young man -- as you're going to find,” Mariners manager Scott Servais said. “He treats everybody with super all kinds of respect. But when it's his day to pitch and he steps out of the dugout to take the mound, it is on, and I love that about him.”

Even Gilbert's teammates who grew up alongside him in the Minors, including catcher Cal Raleigh, were wowed.

“The reaction was awesome,” Raleigh said. “For him to come through in that moment is huge. And for him to gear back and be sitting 99 [mph] for those last couple batters was really impressive. That's like Justin Verlander stuff.”

Through pent-up frustration over shaky fastball command and the stakes of the moment, Gilbert -- or “Walter” -- made the first of what could be many appearances as each passing game becomes increasingly important in Seattle's postseason push.

“I think it was a culmination of that -- close game, just a big moment and trying to make a big pitch,” Gilbert said. “And then when I did, it just kind of came out. I don't even know what happened. I kind of just like blacked out.”

Despite the box score, dramatic finish and consecutive starts without allowing a run, Gilbert felt like he was “off” on Tuesday. He threw first-pitch strikes to only 11 of the 24 White Sox batters he faced, had to labor back into counts and overcame what Servais called “non-competitive pitches.” Yet, Gilbert's ability to navigate through the sixth without his best stuff underscored, in the Mariners’ eyes, how far he’s come.

Gilbert gave up five hits, walked none and struck out a career-high-tying nine, outdueling two-time All-Star Johnny Cueto, who stymied Seattle’s bats and allowed only one run, which came on a throwing error by right fielder Gavin Sheets. Gilbert’s resilience and mid-game adjustments are a huge reason why the Mariners are 18-10 when he pitches -- and why he’d be such a valuable piece in the postseason.

Gilbert's four-seam fastball is his favorite pitch, but the refinement of his slider via a new grip has been huge. He induced whiffs on five of the 10 swings he generated on the breaking ball, four for strikeouts.

“I think as he gets more and more experience, you're only going to see more consistency with that -- because he likes to compete,” Servais said. “He knows he's one of the better pitchers in the league.”

Since getting roughed up a bit by the Astros and Yankees twice apiece out of the All-Star break, Gilbert has hit a stride eerily similar to one last September. Over his past five starts (including Tuesday), he has a 2.15 ERA and has held hitters to a .239/.274/.303 slash line, with a 24.6-percent strikeout rate and 4.2-percent walk rate. Gilbert also hasn’t allowed a homer during this stretch.

Gilbert and the Mariners received a big boost, after the righty left the game, from Raleigh, whose 23rd homer of the year came in the eighth and provided vital insurance, despite Seattle’s collective shutout. Beyond Gilbert, Mariners pitchers have allowed three or fewer runs in nine straight games, the second-longest streak in franchise history behind only a 13-game run in 2014. Gilbert contributed to two of those, as he also tossed six scoreless innings in Detroit last Thursday.

That blowout victory didn’t feature “Walter"; the moment didn’t call for it. But as the calendar gets deeper into September -- and potentially October -- the secret might be out on Gilbert’s incredibly competitive alter ego.