Portillo, the Padres' No. 18 prospect yielded just two hits over a career-high seven shutout innings for Class A Fort Wayne. He was nearly matched by West Michigan starter Carreno, who took a no-hitter into the sixth.
Ultimately, though, neither one factored into the decision as the Whitecaps beat the TinCaps, 2-1, on a walk-off homer by West Michigan's Aaron Westlake in the 11th inning.
Portillo struck out six while issuing just one walk, lowering his ERA from 2.22 to 1.72. The outing marks just the second time he's eclipsed the five-inning threshold this year.
"He had great rhythm and tempo, which is one of the things he's really been working on," Fort Wayne pitching coach Willie Blair said. "His command tonight was excellent. He was able to throw his fastball, breaking ball and changeup for strikes. He mixed his pitches well and he just really had a great all-around game."
Carreno, meanwhile, ended up allowing one run on one hit over six frames. His ERA stands at 3.30.
"I was very happy" he said through a translator. "I'm very happy with the work I've done and am continuing to do."
Portillo gave up his first two hits early, yielding a two-out single to Brandon Loy in the second and a one-out base knock to Jeff Holm in the third. He also issued a two-out walk to Eugenio Suarez in the third, but worked out of trouble by striking out Dean Green.
The 20-year-old right-hander was perfect for the rest of the day, retiring the final 12 batters he faced. He struck out four while allowing just two balls out of the infield during that stretch.
"Even though he gave up a couple hits early, it wasn't like they were on him," Blair said. "You're going to give up hits if you're around the plate, and he was around the plate all night. He did get stronger and more confident as the game went on. His stuff was really dominant."
Carreno started strong, but did not finish as well. He allowed only two baserunners through his first five innings -- a two-out walk to Casey McElroy in the first and a plunking of Mike Gallic to lead off the fifth. He faced just one batter over the minimum in that time, thanks to a double-play ball in the fifth, and garnered five groundouts in total.
"I try to do that," Carreno said. "I try to pitch just a little bit below the strike zone."
The trouble for Carreno came in the sixth when Jace Peterson drew a two-out walk and then stole second. Justin Miller then came through with the TinCaps' first hit of the day, singling on a fly ball to center field to drive in the run.
"I lost a little bit of concentration," Carreno said. "That's when they got it. With [Miller], they were all fastballs."
Carreno induced a flyout by McElroy to end the inning, then was replaced by reliever Jade Todd. Overall, the Whitecaps bullpen tossed five scoreless innings, giving up three hits and striking out six.
Fort Wayne's bullpen was not as strong. Daniel Cropper and Luis De La Cruz combined to surrender two runs on five hits over 3 1/3 frames, including the game-winner homer to Westlake with one out in the 11th.
"I was just waiting for my team to come through and make that final winning run," Carreno said. "It was just a matter of waiting it out. ... I was so happy, I ran out [on the field.]"
Looking toward the rest of the season, Carreno said he wants to continue his success while moving up.
"I want to go up the ladder, go up another level," he said. "Just continue doing well and staying strong."
According to Blair, Portillo needs to continue fine-tuning his game as he tries to realize his potential.
"As far as the rest of the year, I'd look for him to just keep improving his command and his off-speed pitches and just get more consistent," Blair said. "I think if he does that, things are going to be just fine.
"He's a very intelligent kid, nobody works harder than he does. He's super-competitive and he has a will and a desire to get better. He's a great teammate and competes as hard as anyone I've ever had. He's got a ton of upside, there's really no ceiling. He can be as good as he wants to be."