SEATTLE -- Slowly but surely, the growing pains of a young pitcher finding his way and navigating through big league lineups has begun to catch up with Logan Gilbert.

Seattle’s 24-year-old right-hander struggled to find the feel of his secondary pitches in Sunday’s series finale against the Blue Jays, relied heavily on his fastball and was hit hard, given his predictability. Gilbert allowed five runs for the first time since 2019, when he was in Double-A, and the Mariners dropped the finale against the Blue Jays, 8-3, at T-Mobile Park.

• Box score

With the loss, Seattle fell to one game back of Toronto in the American League Wild Card chase. Both the Red Sox, who hold the second spot, and Yankees, the first team on the outside looking in, won on Sunday, which pushed Seattle to 5 1/2 games out of the final postseason spot -- precisely where it was when opening this 4-2 homestand.

As recently as one month ago, Gilbert looked like he could steamroll his way into the American League Rookie of the Year Award conversation. But he now finds himself needing to adjust back to the big leagues adjusting to him.

Gilbert worked a 1-2-3 first inning, but he needed 36 pitches to get through the second, when he gave up a leadoff home run to Teoscar Hernández and a two-run homer to Randal Grichuk, with a nine-pitch single to Corey Dickerson in between. After the homers, Mariners catcher Cal Raleigh worked more breaking balls into the game plan, but it was clear that Gilbert lacked feel for those offerings -- as has been the case in three straight starts.

“They were hunting the fastball and trying to just look for something out over the plate, especially if I didn't get the slider in-zone,” Gilbert said. “I feel like the main thing is just proving that in the zone, especially early in the game, and then from there, I can expand. But they did a good job just hunting the fastball in the zone, and I wasn't able to make the adjustments today.”

Before Gilbert was sent back out for the fourth, Mariners manager Scott Servais told Gilbert that it would likely be his final frame -- and he encouraged the 6-foot-6 righty to ignore the score and deliberately throw more offspeed stuff to seek out the feel of those pitches. One of those resulted in a single for No. 9 hitter Santiago Espinal, but another brought his third strikeout of All-Star Bo Bichette, his final batter of the day.

“The focus, you’ve still got to control counts,” Servais said. “And you can't just keep throwing pitches and pitches. Obviously, he needs to continue to work on it. I actually thought some of the sliders he did throw today, I liked the shape of it. I like where it's headed. It's coming out a little bit firmer, a little bit harder. But you’ve got to challenge with it in the strike zone.”

Servais said recently that Gilbert’s curveball -- which was touted as his best secondary pitch in the Minors -- remains a work in progress, largely because it was coming out of a different arm slot.

“He was trying to make it nasty, was trying to get on top of it, and it really was going the opposite way,” Servais said. “It wasn't looking like the rest of his pitches, and that's why they weren't swinging at it and he was having a hard time dropping it in for a strike, so he's made some adjustments with it.

Here’s an illustration of what Servais is describing -- the turning point appears to be Gilbert's June 26 start vs. the White Sox in Chicago that was cut short due to weather:

“Sometimes it's been there, sometimes it hasn't,” Servais said. “What we've really seen the growth in is his slider. That's a pitch he's leaned on more heavily than the curveball. The curveball has probably been his most inconsistent pitch, but the slider and changeup are the ones he's leaned on.”

Yet, the changeup, which has been borderline unhittable at times, was essentially absent Sunday, as Gilbert threw it only three times. And the slider wasn’t exactly on, either. Of the season-high eight hits Gilbert gave up, three were on his slider, all singles, and the other five were on his four-seam fastball, including both homers.

“It's tough. I mean, the main thing is just making an adjustment, which we talked [about] going into the fourth, [which] was a little better,” Gilbert said. "Adjusting the sight lines on a pitch and bringing it up, especially when I was missing out of the zone low. But you can't just lay anything up there over and over. You’ve got to find a way to make an adjustment and get the feel during the outing.”

The Mariners have lost each of Gilbert’s past three starts after winning 11 in a row from mid-May through the end of July, the longest stretch any team has won behind one starter since Gerrit Cole’s stretch of 13 to end the 2019 season for the Astros. Sunday also snapped a 14-game streak dating back to July 31 in which a Seattle starter had given up three or fewer runs.

Gilbert has shown glimpses of greatness in his promising rookie season, but like just about any young pitcher -- and especially against an elite lineup like Toronto's -- he’s still learning and growing.