It’s been an interesting season for No. 10 Oregon State baseball’s Nelson Keljo.

The left-handed junior entered the 2025 campaign as the anointed ace of the Beavers staff after dominating late-innings for head coach Mitch Canham’s bullpen as a sophomore. Keljo threw 11-scoreless innings in his final four appearances during Oregon State’s 2024 postseason run, punching out 15 batters while allowing just two hits and a single walk.

His ascension to the weekend rotation and the fanfare that came with it wasn’t limited to just Corvallis and the Beaver faithful, but caught the attention of professional baseball as well. Keljo debuted at No. 89 on MLB Pipeline’s Top 100 draft prospects rankings, one of five Beavers on the preseason list. Expectations were big for the southpaw from Portland’s Jesuit High School.

And understandably so. Who wouldn’t want a 6-foot-4, 220-pound lefty throwing an upper-90s fastball with elite run, as well as secondary offerings of a slider and changeup?

But, as already said, it’s been an interesting year. Working back-to-back with right-hander Eric Segura out of the pen, Keljo worked four innings in each of his first three starts in 2025, facing Xavier, Virginia and Baylor. Keljo allowed just four runs across the three, but never went deep enough in a start to earn a decision as his pitch-count was being built up. Back-to-back starts at home against San Diego and Grand Canyon saw Keljo work into decision territory for the first time all year, going five-deep against the Torreros and six full against the Antelopes.

With 12 strikeouts to just six hits, four walks and no runs — earned or unearned — in those outings, it looked like Keljo had arrived.

That was until a minor injury saw him lifted from a start at Cal Poly after just three innings and 57 pitches, missing his start the next weekend at Nebraska for precautionary reasons. After returning for a home start against UC Irvine on April 4, the Anteaters ran Keljo off the mound in the top of the second inning. The lefty hasn’t pitched more than 4.2 innings in a start since, allowing 13 earned runs in 17.2 frames over his last four starts.

He also was no longer featured on Pipeline’s top prospects list, which expanded from 100 prospects to 200 in its most-recent update. Baseball America’s 400-deep list had the left-hander out of its top-100, falling to No. 276. On the most bird’s-eye view, surface level stage in the sport, it looked like baseball had seen enough of Keljo the starting pitcher.

After being swept in four games by Oregon, Canham and his coaching staff made the decision to give the weekend rotation a shakeup. Segura got the ball for a Friday, May 2 start against Hawai’i, with right-hander Dax Whitney and lefty Ethan Kleinschmit standing pat in their respective Saturday and Sunday starting roles. Keljo was back to the bullpen.

Oregon State moved off of its piggyback model for Segura and Keljo for at least its series against the Rainbow Warriors, too. Right-handed relievers AJ Hutcheson (2.1 innings) and Kellan Oakes (1.2 IP, 4 Ks) finished off an 11-4 win on Friday after Segura logged five frames of four-run (two earned) ball in the start. Oregon State’s big lefty wouldn’t have to wait long for his opportunity.

Come the bottom of the fifth inning on Saturday, Whitney let up a run to give Hawai’i a 2-0 lead before walking the next batter on four pitches. With two runners aboard and the Rainbow Warriors three-hole hitter Ben Zeigler-Namoa coming up, Oregon State went to its bullpen and out came the left-hander, No. 36, Nelson Keljo.

What transpired was some of the best pitching Keljo had put on paper all season long. He sent Zeigler-Namoa down swinging to escape the jam before embarking on a 4.1-inning stint to finish off a 3-2 win over Hawai’i. The left-hander allowed just one hit — a leadoff double in the bottom of the sixth — and walked two while striking out four.

Keljo got the final out in the bottom of the ninth in style, blowing a third-strike fastball by Hawai’i catcher Hunter Falido. The three-pitch strikeout sealed the win for Oregon State, even after a leadoff walk and a steal of second base by Hawai’i left fielder Kamana Nahaku put the tying run in scoring position.

The final pitch of his dominant relief outing — and, seemingly, return to form — came at 12:29 a.m. in Corvallis on May 4, exactly one month since his skid began against UC Irvine.

“Fastball taken, strike three called!” Beavers Radio Network’s Mike Parker, the voice of Oregon State baseball, said on his play-by-play call on the game, which was not not televised or broadcast.

“And Keljo does take care of business!” Parker said. “He hugs (catcher and battery mate) Wilson Weber, he strikes out Hunter Falido to end the game on a sensational note. With the tying run at second base, Nelson Keljo — in perhaps his finest outing of the year — comes through with the win.”

Keljo appeared on Parker’s pre-game show ahead of a 5-0 loss by Oregon State to Hawai’i on Sunday, breaking down the win he earned the night prior. The left-hander acknowledged his month-long skid, saying being bumped from the rotation wasn’t a bother, but an opportunity to reset.

“I just want to do what I can to help the team win and put (us) in the best position possible,” Keljo told Parker on the Beavers Sports Network. “I’ve had a little rough patch this past month, so getting (out of it), getting back into (rhythm) and maintaining my confidence (is the goal).”

It’s also been an opportunity for the left-hander to work on his arsenal. Keljo told Parker that while his fastball remains the king of his three-pitch mix, he’s swapped his slider for a curveball and was happy with the results against the Rainbow Warriors.

“The fastball felt good, that’s kind of always there for me,” Keljo said. “I’ve had some trouble this year with my slider, that’s kind of been the main reason why I’ve been walking people. My slider strike percentage is below 45%, so that’s gotten me behind in counts and whatnot. (Pitching coach Rich Dorman) has been helping me this past week with a shorter curveball grip.

“I can just rip that, instead of having to manipulate the slider. I feel like I throw it better in the zone for strikes and can get some swing-and-miss whiffs on it. That really helped, I was able to throw it for some strikes, land it in there and burry it down in the zone for swing-and-miss… My changeup also felt better, so if I can have those three pitches working, it’ll be really good.”

Keljo finished the interview with Parker saying honing in his command of the strike zone and the base paths are still his biggest focuses, walking the pair of batters and letting up two steals in his outing. But if the junior can replicate the performance out of the pen — if he doesn’t graduate back into the weekend rotation — over the coming weekends and into the postseason, Oregon State might have found itself a left-handed anchor in relief.